feat(web): enhanced file panel — side-by-side diff, hide whitespace, inline review

Adds DiffSplitView component for side-by-side diff mode, whitespace-only
change filtering, inline review comments with thread/gutter cell UI, diff
preferences persistence, and write-file API support for in-browser editing.

Backend: hideWhitespace param on git diff endpoint, write_file route.

apps/web/src/api/client.ts

@@ -30,6 +30,10 @@ import type {
   BattleShape,
   ContestantShape,
   CrossExaminationShape,
+  AnalyticsSummary,
+  SessionAnalyticsRow,
+  ContextWindowStats,
+  TokenBreakdownAgg,
 } from './types';
 
 // v2.6 Phase 1-UX §9b: chat-scoped agent-session rows. Returned by
@@ -159,12 +163,13 @@ export const api = {
       request<{ files: string[] }>(`/api/projects/${id}/files`),
     git: (id: string) =>
       request<GitMeta>(`/api/projects/${id}/git`),
-    gitDiff: (id: string, mode: GitDiffMode | null) =>
-      request<GitDiffResult>(
-        mode !== null
-          ? `/api/projects/${id}/git/diff?mode=${mode}`
-          : `/api/projects/${id}/git/diff`,
-      ),
+    gitDiff: (id: string, mode: GitDiffMode | null, hideWhitespace?: boolean) => {
+      const params: string[] = [];
+      if (mode !== null) params.push(`mode=${mode}`);
+      if (hideWhitespace) params.push('whitespace=1');
+      const qs = params.length > 0 ? `?${params.join('&')}` : '';
+      return request<GitDiffResult>(`/api/projects/${id}/git/diff${qs}`);
+    },
     gitStage: (id: string, files: string[]) =>
       request<{ ok: boolean }>(`/api/projects/${id}/git/stage`, {
         method: 'POST',
@@ -185,6 +190,11 @@ export const api = {
         method: 'POST',
         body: JSON.stringify({ files }),
       }),
+    writeFile: (id: string, filePath: string, content: string) =>
+      request<{ ok: boolean }>(`/api/projects/${id}/write_file`, {
+        method: 'POST',
+        body: JSON.stringify({ path: filePath, content }),
+      }),
   },
 
   sessions: {
@@ -590,6 +600,14 @@ export const api = {
     costStats: () => request<{ stats: ToolCostStat[] }>('/api/tools/cost_stats'),
   },
 
+  // token-analyzer-ui: analytics aggregate endpoints.
+  analytics: {
+    summary: () => request<AnalyticsSummary>('/api/coder/analytics/summary'),
+    sessions: () => request<{ sessions: SessionAnalyticsRow[] }>('/api/coder/analytics/sessions'),
+    context: () => request<ContextWindowStats>('/api/analytics/context'),
+    tokenBreakdown: () => request<{ categories: TokenBreakdownAgg[] }>('/api/coder/analytics/token-breakdown'),
+  },
+
   settings: {
     get: () => request<Record<string, unknown>>('/api/settings'),
     patch: (body: Record<string, unknown>) =>