feat(browser): replace the preview proxy with a real browser panel and an agent web tool (#2883)

The preview panel worked by proxying a dev server through OpenChamber's own
origin and rewriting the HTML that came back. Anything the rewriter did not
anticipate broke, and pages that refuse to be embedded never loaded at all.
This deletes the proxy (-1604 lines and its tests) and merges the preview and
browser panels into one surface backed by a real Chromium view.

What the panel is now

- A `<webview>` in its own session partition: logins and cookies persist, hot
  reload works because nothing is rewritten, DevTools are one click away.
- Annotation: pick one element, drag a region, or draw freehand, write a note,
  and it reaches chat with a screenshot of the visible page with the marks on it.
- Toolbar: hard reload, page zoom, device sizes, a light/dark switch that
  applies to the page rather than the app, and cookie/cache clearing scoped to
  the panel alone.
- Several pages at once, each tab showing the page's own favicon, and an address
  bar that suggests pages already visited in this project.
- Dev servers are listed from what is actually listening on the machine, checked
  against what a project announced, so a server is offered no matter how it was
  started. One that is still starting is waited for instead of failing.

Remote dev servers

The desktop app binds a local port and pipes raw bytes to the OpenChamber host
over the existing authenticated connection, so the page keeps its own origin at
the root of its own host. The reachable set is exactly what discovery reports
and is re-checked per connection, so an authenticated client cannot dial
arbitrary local services on the host. Links and redirects to another loopback
port stay on the machine that served the page. A tunnel that cannot be opened is
reported; it is never replaced by the plain loopback URL, which would answer
from the user's own machine under a remote address.

Agent control

Browser actions are a separate `openchamber_web` tool: open, snapshot, click,
type, scroll, inspect computed styles, resize between mobile/tablet/desktop, and
capture a screenshot into `.openchamber/screenshots/` in the project. The
existing `openchamber` tool keeps sessions, worktrees and scheduled tasks. Each
has its own setting in the new Settings -> General -> OpenChamber Tools section,
and the plugin is not injected at all when both are off.

Capability belongs to the connected client, not to configuration: a client
declares on its event stream that it can drive a page, which only a Chromium
host does. Exactly one client performs each request — it claims the request
before acting, and the first claim wins — because deciding by whose result
arrives first would be too late for a click that already happened. No client
listening is answered immediately with an explanation rather than a timeout.

Runtime boundaries

Web tabs get a plain iframe that can display a page but not inspect one. The
VS Code extension no longer offers the surface at all, since nothing that makes
the panel worth having works there. Mobile is unaffected.

Native boundary

Camera, microphone, location and device-picker requests from panel pages are
denied — Electron grants them by default when no handler is set, and the panel
loads whatever address the user types. Page capture, appearance emulation and
storage clearing verify that their target belongs to the panel's own session
instead of trusting a web-contents id from the renderer.

Persisted state

Stored `preview` tabs migrate to `browser` (v13 -> v14). Context panel tab
limits are now per surface, so filling one surface no longer evicts another's
tabs. Address history is stored per project and per runtime.

Documentation

`preview.mdx` and `desktop-browser.mdx` rewritten across all locales, the agent
tool settings path corrected, new `DOCUMENTATION.md` for the browser-control
broker and the dev tunnel, and the `ui-api-decoupling` skill updated where it
still described the deleted proxy.

packages/ui/src/lib/i18n/messages/pt-BR.ts

@@ -1196,9 +1196,62 @@ export const dict: Record<I18nKey, string> = {
   "contextRail.editorTree.toggle": "Alternar árvore de arquivos",
   "contextPanel.browser.open": "Abrir painel do navegador",
   "contextPanel.browser.addressAria": "Endereço do navegador",
+  "contextPanel.browser.history.label": "Endereços recentes",
+  "contextPanel.browser.history.forget": "Remover do histórico",
+  "contextPanel.browser.newTab": "Nova aba do navegador",
   "contextPanel.browser.empty": "Navegador web",
   "contextPanel.browser.emptyHint": "Digite um endereço acima para começar a navegar",
   "contextPanel.browser.inspectUnavailable": "Esta página não pode ser inspecionada pelo painel do navegador.",
+  "contextPanel.browser.back": "Voltar",
+  "contextPanel.browser.forward": "Avançar",
+  "contextPanel.browser.reload": "Recarregar",
+  "contextPanel.browser.hardReload": "Recarregar ignorando o cache",
+  "contextPanel.browser.zoomIn": "Ampliar",
+  "contextPanel.browser.zoomOut": "Reduzir",
+  "contextPanel.browser.zoomReset": "Redefinir zoom",
+  "contextPanel.browser.clearCookies": "Limpar cookies",
+  "contextPanel.browser.clearCache": "Limpar cache",
+  "contextPanel.browser.clearedCookies": "Cookies limpos",
+  "contextPanel.browser.clearedCache": "Cache limpo",
+  "contextPanel.browser.clearFailed": "Não foi possível limpar os dados de navegação",
+  "contextPanel.browser.stop": "Parar",
+  "contextPanel.browser.openExternal": "Abrir no navegador do sistema",
+  "contextPanel.browser.devTools": "Abrir DevTools",
+  "contextPanel.browser.deviceToolbar": "Barra de dispositivos",
+  "contextPanel.browser.device.preset": "Predefinição de dispositivo",
+  "contextPanel.browser.device.responsive": "Responsivo",
+  "contextPanel.browser.device.width": "Largura da viewport",
+  "contextPanel.browser.device.height": "Altura da viewport",
+  "contextPanel.browser.device.rotate": "Girar",
+  "contextPanel.browser.device.schemeSystem": "Auto",
+  "contextPanel.browser.device.schemeLight": "Claro",
+  "contextPanel.browser.device.schemeDark": "Escuro",
+  "contextPanel.browser.device.schemeFailed": "Não foi possível mudar a aparência da página",
+  "contextPanel.browser.frameTitle": "Navegador",
+  "contextPanel.browser.loadFailed": "Não foi possível carregar esta página",
+  "contextPanel.browser.waitingForServer": "Aguardando o servidor de desenvolvimento",
+  "contextPanel.browser.waitingForServerHint": "Ele ainda não aceita conexões. A página carregará assim que aceitar.",
+  "contextPanel.browser.tunnelFailed": "Não foi possível alcançar este servidor de desenvolvimento",
+  "contextPanel.browser.tunnelFailedHint": "{url} roda na máquina onde o OpenChamber está e não foi possível abrir a conexão com ela. Nada da sua própria máquina é mostrado aqui.",
+  "contextPanel.browser.loadFailedUnknown": "Não foi possível acessar a página.",
+  "contextPanel.browser.crashed": "Esta página parou de responder",
+  "contextPanel.browser.crashedHint": "A página falhou várias vezes seguidas. Recarregue para tentar de novo.",
+  "contextPanel.browser.devServers.title": "Servidores de desenvolvimento em execução",
+  "projectActions.toast.multipleServers": "Vários servidores iniciaram — escolha um no painel do navegador",
+  "contextPanel.browser.devServers.justStarted": "Recém-iniciados",
+  "contextPanel.browser.devServers.unavailable": "Não foi possível verificar os servidores de desenvolvimento em execução.",
+  "contextPanel.browser.devServers.remoteOnly": "Eles rodam na máquina que hospeda o OpenChamber. Abri-los exige o aplicativo desktop.",
+  "contextPanel.browser.annotate.toggle": "Anotar página",
+  "contextPanel.browser.annotate.intro": "Esta é uma seleção anotada do navegador integrado.",
+  "contextPanel.browser.annotate.attached": "Anotação anexada ao chat",
+  "contextPanel.browser.annotate.noSession": "Abra uma sessão de chat antes de anexar uma anotação",
+  "contextPanel.browser.annotate.noPage": "Carregue uma página antes de anotar",
+  "contextPanel.browser.annotate.failed": "Não foi possível anotar esta página",
+  "contextPanel.browser.annotate.tool.element": "Elemento",
+  "contextPanel.browser.annotate.tool.region": "Região",
+  "contextPanel.browser.annotate.tool.draw": "Desenhar",
+  "contextPanel.browser.annotate.commentPlaceholder": "Descreva a mudança...",
+  "contextPanel.browser.annotate.submit": "Anexar",
   "contextPanel.browser.trustNotice": "As páginas abertas aqui são executadas com acesso total ao OpenChamber — necessário para inspeção e capturas de tela. Abra apenas sites confiáveis: uma página maliciosa pode ler seus dados ou agir em seu nome.",
   "contextPanel.tab.closeTabAria": "Fechar aba {label}",
   "contextPanel.actions.collapsePanel": "Recolher painel",