perf: cut cold-start download 58% and startup heap 22% via measured chunk-graph fixes (#2742)

* fix(ui): update session-switch-resync test to current handleEvent/setSessionTodos signatures

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(build): split Shiki grammars/themes, CodeMirror legacy modes, and @pierre/diffs into on-demand chunks

Merging @shikijs/langs into one manual vendor chunk made the first language
request download every grammar (7.4 MB raw / 1 MB gzip). Letting Rollup split
these packages per dynamically imported module downloads only the languages,
themes, and modes actually used — matching how the worker build already
behaves. @pierre/diffs is split the same way so its pure patch parser (used by
the eager tool renderer) no longer drags the Shiki-importing render stack into
the startup graph.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(ui): restore lazy heavy views and stop eager settings-graph loading

- MainLayout: DiffView/FilesView/GitView/PlanView return to lazyWithChunkRecovery
  (they were silently made static in 2031e3b4 while their Suspense wrappers
  remained), keeping the CodeMirror and @pierre/diffs stacks out of startup.
- ContextPanel: same lazy treatment for its Diff/Files/Git/Plan/Walkthrough
  tabs, with null Suspense fallbacks.
- CommandPalette imported getSettingsNavIcon from SettingsView, statically
  pulling the entire settings surface (SkillsPage -> CodeMirrorEditor -> vim
  mode, theme registry -> @pierre/diffs) into the eager graph; the helper now
  lives in lib/settings/metadata.
- The windowed SettingsWindow mounts only after its first open: rendering the
  lazy component closed made React fetch the SettingsView chunk graph at
  startup.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(ui): keep @pierre/diffs + Shiki out of the eager chat graph and defer diff worker warmup

- DiffWorkerProvider no longer statically imports @pierre/diffs/worker or the
  theme registry, and no longer spawns 3 workers plus a main-thread shared
  highlighter during mount. Pools are created on demand through a dynamic
  module load, warmed via requestIdleCallback after startup settles, and
  useWorkerPool notifies consumers when a pool becomes available.
- ToolPart's rich diff preview moves to lazily loaded ToolPartDiffPreview;
  the plain-text patch (PlainDiffFallback) renders while the chunk loads,
  mirroring the existing error fallback. Theme registration happens during
  render inside the lazy module so PatchDiff never renders unregistered ids.
- ChatInput mounts its lazy ToolOutputDialog only after the first attachment
  preview opens instead of fetching the dialog chunk on the draft screen.
- getMarkdownSyntaxVars moves to a pierre-free markdownSyntaxVars module so
  eager code-rendering consumers stop importing the registration module.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(web): load ghostty-web and Nerd Fonts on first terminal use

- ghostty-web (638 KB raw JS + WASM VT) is dynamically imported when a
  terminal actually mounts; TerminalView stays eagerly importable for the
  bottom dock.
- The ~2 MB of CDN Nerd Fonts are no longer preloaded and force-loaded on
  every cold start. index.html exposes an idempotent
  __openchamberEnsureNerdFonts hook; TerminalViewport requests it on mount
  and waits up to 2s so a cached font is in place before the glyph atlas is
  built, while a cold CDN fetch never blocks the terminal. Runtimes without
  the hook (VS Code, mobile) resolve immediately, matching their existing
  fallback-font behavior.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

---------

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/lib/settings/metadata.ts

@@ -1,4 +1,5 @@
 import type { SidebarSection } from '@/constants/sidebar';
+import type { IconName } from '@/components/icon/icons';
 
 export type SettingsPageSlug =
   | 'home'
@@ -237,3 +238,65 @@ export function resolveSettingsSlug(value: string | null | undefined): SettingsP
 
   return 'home';
 }
+
+// Lives here (not in SettingsView) so light consumers such as the command
+// palette can render settings entries without statically importing the whole
+// settings surface into the eager startup graph.
+export function getSettingsNavIcon(slug: SettingsPageSlug): IconName | null {
+  switch (slug) {
+    case 'general':
+      return 'settings-3';
+    case 'projects':
+      return 'folders';
+    case 'remote-instances':
+      return 'computer';
+    case 'appearance':
+      return 'palette';
+    case 'chat':
+      return 'chat-ai-3';
+    case 'magic-prompts':
+      return 'ai-generate-2';
+    case 'snippets':
+      return 'chat-thread';
+    case 'notifications':
+      return 'notification-3';
+    case 'shortcuts':
+      return 'command';
+    case 'sessions':
+      return 'chat-history';
+
+    case 'providers':
+      return 'cloud';
+    case 'agents':
+      return 'ai-agent';
+    case 'behavior':
+      return 'brain';
+    case 'commands':
+      return 'slash-commands-2';
+    case 'mcp':
+      return null;
+    case 'plugins':
+      return 'plug-2';
+
+    case 'skills.installed':
+      return 'book-open';
+    case 'skills.catalog':
+      return 'book';
+
+    case 'git':
+      return 'git-branch';
+
+    case 'usage':
+      return 'bar-chart-2';
+    case 'voice':
+      return 'mic';
+    case 'tunnel':
+      return 'home-office';
+    case 'about':
+      return 'information';
+    case 'home':
+      return null;
+    default:
+      return 'robot-2';
+  }
+}