feat(web,coder): add analytics + results pages for token usage and run history

New /analytics route: token usage dashboard with aggregate summary,
per-session breakdown, context window stats, and per-category token
distribution. Data served from existing agent_sessions + tool_cost_stats.

New /results route: browsable archive of orchestrator flow runs and
arena battles. Two-tab layout (Analysis Runs / Arena Battles) using
existing API endpoints (no new backend).

Sidebar gains Results (ScrollText icon) and Token Analytics (BarChart3
icon) nav buttons above Settings.

apps/server/src/routes/analytics.ts

@@ -0,0 +1,33 @@
+import type { FastifyInstance } from 'fastify';
+import type { Sql } from '../db.js';
+
+// token-analyzer-ui: context window utilization and token breakdown data.
+// v1 — global aggregates only.
+
+export interface ContextWindowStats {
+  avg_ctx_used: number | null;
+  avg_ctx_max: number | null;
+  avg_utilization_pct: number | null;
+  message_count: number;
+}
+
+export function registerAnalyticsRoutes(app: FastifyInstance, sql: Sql): void {
+  // GET /api/analytics/context — average context window utilization across
+  // completed assistant messages that carry ctx_used/ctx_max.
+  app.get('/api/analytics/context', async () => {
+    const [row] = await sql<ContextWindowStats[]>`
+      SELECT
+        AVG(ctx_used)::DOUBLE PRECISION AS avg_ctx_used,
+        AVG(ctx_max)::DOUBLE PRECISION AS avg_ctx_max,
+        AVG(ctx_used::float / NULLIF(ctx_max, 0))::DOUBLE PRECISION AS avg_utilization_pct,
+        COUNT(*)::INT AS message_count
+      FROM messages
+      WHERE role = 'assistant'
+        AND status = 'complete'
+        AND ctx_used IS NOT NULL
+        AND ctx_max IS NOT NULL
+        AND ctx_max > 0
+    `;
+    return row ?? { avg_ctx_used: null, avg_ctx_max: null, avg_utilization_pct: null, message_count: 0 };
+  });
+}