perf: lazy-load heavy dependencies (MarkdownRenderer + CodeMirror languages) (#997)

* perf: drastically improve cold-start, bundle size, and streaming performance

Cold-start optimizations:
- main.tsx: Remove blocking await on prefs I/O — render immediately with
  defaults, hydrate persisted settings asynchronously. Cuts 50-200ms from
  time-to-first-paint.
- bootstrap.ts: Split directory bootstrap into 3 phases:
  * Phase 1 (blocking): path, config, provider, session status — minimum
    data needed to render UI. Mark status complete after this phase.
    path.get and session.status must both succeed; they have no fallback.
  * Phase 2 (deferred): agents, commands, mcp, lsp, vcs, questions,
    permissions — fetched after first paint without blocking.
  * Phase 3 (lazy): session messages — loaded without blocking init.
- App.tsx: Keep identical provider tree before/after init to prevent
  full subtree remount when isInitialized flips. FireworksProvider and
  VoiceProvider are lightweight shells; overlays deferred until init.

Bundle-size optimizations:
- App.tsx + MainLayout.tsx + VSCodeLayout.tsx: Code-split heavy views
  (SettingsView, GitView, DiffView, TerminalView, FilesView, PlanView,
  OnboardingScreen, SettingsWindow, MultiRunWindow) with React.lazy.
  Views load on demand when user switches panels.
- vite.config.ts: Lower chunkSizeWarningLimit from 1200KB to 500KB.

Streaming render optimizations:
- streaming.ts: Throttle streaming store writes ~60Hz → ~1Hz. Busy-session
  only scan (Set, O(1)).
- MessageList.tsx: Lower virtualization threshold 40 → 15.
- ChatMessage.tsx: React.memo with areRenderRelevantMessagesEqual.
- MarkdownRenderer.tsx: React.memo with explicit prop comparators.

* fix: address Greptile review feedback on bootstrap and provider tree

- bootstrap.ts: Tighten Phase 1 error guard. path.get and session.status
  must both succeed; they have no global fallback.
- bootstrap.ts: Replace dead .catch() on Promise.allSettled() with .then()
  that inspects individual results for errors.
- App.tsx: Keep identical provider tree before/after init to prevent full
  subtree remount when isInitialized flips.

* perf: lazy-load heavy dependencies (MarkdownRenderer + CodeMirror languages)

MarkdownRenderer dynamic import:
- Move heavy implementation (marked, react-markdown, beautiful-mermaid,
  react-syntax-highlighter, ~1500 lines) to MarkdownRendererImpl.tsx
- Replace MarkdownRenderer.tsx with thin lazy wrapper using React.lazy
- All 11 existing imports work unchanged — no consumer code modified
- Full markdown stack loads on first render of markdown content

CodeMirror language lazy loading:
- languageByExtension.ts: remove static imports for 10+ less-common
  language packages (@codemirror/lang-go, lang-rust, lang-sql, etc.)
- Keep only 6 most common languages static: javascript, json, css, html,
  markdown, python, shell
- Less common languages return null from languageByExtension, causing
  callers to fall back to loadLanguageByExtension which dynamically
  loads from @codemirror/language-data
- Reduces initial bundle by ~200KB+ of language parsers

---------

Co-authored-by: Shyamalan Kannan <yabuku@Shyamalans-MacBook-Pro.local>

packages/ui/src/components/layout/VSCodeLayout.tsx

@@ -1,7 +1,9 @@
 import React from 'react';
 import { ErrorBoundary } from '../ui/ErrorBoundary';
 import { SessionSidebar } from '@/components/session/SessionSidebar';
-import { ChatView, SettingsView } from '@/components/views';
+import { ChatView } from '@/components/views';
+
+const SettingsView = React.lazy(() => import('@/components/views/SettingsView').then(m => ({ default: m.SettingsView })));
 import { useSessionUIStore } from '@/sync/session-ui-store';
 import { useViewportStore } from '@/sync/viewport-store';
 import { useSessions, useDirectorySync } from '@/sync/sync-context';
@@ -388,10 +390,12 @@ export const VSCodeLayout: React.FC = () => {
         </div>
       ) : currentView === 'settings' ? (
         // Settings view
-        <SettingsView
-          onClose={() => setCurrentView(usesExpandedLayout ? 'chat' : 'sessions')}
-          forceMobile={usesMobileLayout}
-        />
+        <React.Suspense fallback={null}>
+          <SettingsView
+            onClose={() => setCurrentView(usesExpandedLayout ? 'chat' : 'sessions')}
+            forceMobile={usesMobileLayout}
+          />
+        </React.Suspense>
       ) : usesExpandedLayout ? (
         // Expanded layout: sessions sidebar + chat side by side
         <div className="flex h-full">