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/components/chat/ChatInput.tsx

@@ -32,7 +32,7 @@ import {
 } from '@/lib/chatDraftPersistence';
 import { ReviewFlowDialog, type ReviewFlowExecution } from '@/components/session/ReviewFlowDialog';
 import { AttachedFilesList, AttachedVSCodeFileChips, ActiveEditorFileSuggestion } from './FileAttachment';
-import ToolOutputDialog from './message/ToolOutputDialog';
+import { lazyWithChunkRecovery } from '@/lib/chunkLoadRecovery';
 import type { ToolPopupContent } from './message/types';
 import { QueuedMessageChips } from './QueuedMessageChips';
 import { AutoReviewBanner } from './AutoReviewBanner';
@@ -142,6 +142,10 @@ import { RevertedMessageDock } from './composer/ui/RevertedMessageDock';
 import { SessionSuggestionChip } from '@/components/chat/SessionSuggestionChip';
 import { SessionGoalRow } from '@/components/chat/SessionGoalRow';
 
+// Lazy like in ChatMessage: a static import would pull the @pierre/diffs and
+// Shiki stacks into the eager startup graph for a dialog opened on demand.
+const ToolOutputDialog = lazyWithChunkRecovery(() => import('./message/ToolOutputDialog'));
+
 const MAX_VISIBLE_COMPOSER_LINES = 8;
 /**
  * Mobile grows the composer with content instead of offering a fullscreen
@@ -383,6 +387,15 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
         title: '',
         content: '',
     });
+    // Mount the lazy preview dialog only after its first open; rendering it
+    // closed would fetch the ToolOutputDialog chunk (with the @pierre/diffs
+    // stack) on the draft screen before any preview is requested.
+    const [attachmentPreviewMounted, setAttachmentPreviewMounted] = React.useState(false);
+    React.useEffect(() => {
+        if (attachmentPreview.open) {
+            setAttachmentPreviewMounted(true);
+        }
+    }, [attachmentPreview.open]);
     const attachmentCompatibilityRef = React.useRef({
         modelKey: `${currentProviderId ?? ''}/${currentModelId ?? ''}`,
         modalitySignature: currentModelMetadata?.modalities?.input?.slice().sort().join(',') ?? null,
@@ -2786,11 +2799,15 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
             submitting={reviewFlowSubmitting}
             onConfirm={handleStartReviewFlow}
         />
-        <ToolOutputDialog
-            popup={attachmentPreview}
-            onOpenChange={handleAttachmentPreviewOpenChange}
-            isMobile={isMobile}
-        />
+        {attachmentPreviewMounted ? (
+            <React.Suspense fallback={null}>
+                <ToolOutputDialog
+                    popup={attachmentPreview}
+                    onOpenChange={handleAttachmentPreviewOpenChange}
+                    isMobile={isMobile}
+                />
+            </React.Suspense>
+        ) : null}
 
         {/* Single always-mounted picker input. It must NOT live inside
             ComposerAttachmentControls: that component mounts once per composer