feat(auth): detect session expiry live and offer re-login in place

Every response already funnels through runtimeFetch, so a classifier there
spots 401s, confirms them against /auth/session (a proxied provider 401
must not read as a logout), and flips a small auth-session store. The web
and hosted surfaces show a frosted banner under the header whose Log in
button hands off to the session gate's existing unlock flow; sends are
paused while expired, the session-load error screen explains the auth case
and retries itself after login, and returning to a long-idle window
revalidates once via visibility/focus. Native mobile feeds the same signal
into its connection re-probe instead of showing the banner; VS Code is
exempt.

CHANGELOG.md

@@ -10,6 +10,7 @@ All notable changes to this project will be documented in this file.
 - **Session tabs (opt-in):** the web/desktop header can show your open sessions as browser-style tabs — turn them on in Settings → General → Navigation → Session tabs. Every session you open joins the strip, clicking a tab switches the whole workspace (chat, project, panels), and closing one (its × button, middle-click, or Alt+W — rebindable in Shortcuts) never touches the session itself. Tabs reorder by drag, scroll behind the header buttons when there are many and carry the sidebar's running/unread dot. Each tab has the full session menu — on the "..." button or right-click — plus Close other tabs; renaming works right in the tab.
 - **Keyboard shortcuts learned sequences** (thanks @ChangeHow): shortcuts can now be two steps — press Cmd/Ctrl+S, then a letter: P opens the draft's project picker, G its branch picker, L the session list. A held sequence shows no menu but forgives you: Escape or three quiet seconds cancel it, and typing into a text field never triggers one armed elsewhere. Dropdown menus and pickers now also answer Ctrl+N/Ctrl+P for down/up, the session switcher opens focused on your current session, and every tooltip and menu label shows the binding you actually have set, not the default.
 - **Keyboard shortcuts redesigned.** Defaults now follow one model: single chords for everyday actions, a two-step Cmd/Ctrl+K leader for open/go actions (K then P/G/L — project picker, branch picker, session list; T timeline, N prompt navigator, I services, H shortcut help, C theme), held Cmd/Ctrl+digit for header session tabs and held Cmd/Ctrl+Option+digit for context panel surfaces. Cmd/Ctrl+B now toggles the sidebar; when it's already open, the session-list shortcut jumps into its search. Rare actions moved into the command palette instead of carrying obscure default bindings, and custom bindings recorded under the old layout are reset once. Shortcuts also stopped requiring an English keyboard layout — bindings follow the physical key on non-Latin layouts (and Option-modified digits on macOS), including when recording custom ones.
+- **Session expiry is announced, not discovered.** When the OpenChamber login expires (a browser on the LAN, a paired device, a tunnel), a frosted banner appears under the header within seconds — before anything is clicked — saying the session expired, with a Log in button that opens the usual unlock screen. Work on screen stays visible and interactive; sending is paused until login instead of failing into a toast. A 401 is confirmed against the server first, so an expired model-provider key can't fake a logout, and returning to the app after a long absence re-checks the session once. If a conversation failed to load while logged out, it explains that and reloads itself right after login.
 - **Permission cards answer to the keyboard:** Alt+Enter allows once, Alt+Shift+Enter allows always, Alt+Backspace denies — the keys are printed on the buttons, and the newest pending card is the one that listens. The auto-accept toggle also got a shortcut (Cmd/Ctrl+K, A).
 - Sessions: Cmd/Ctrl+Alt+Left/Right steps back and forward through the sessions you opened in this window, browser-history style; with session tabs enabled it moves between neighbouring tabs instead. Cmd/Ctrl+K, R renames the current session right in the header.
 - Git: Cmd/Ctrl+Enter in the commit message box commits, like every git client.