COD-9 add cross-session search backend (GET /api/search) v1

Bounded federated search over in-memory stores (sessions/cases, run-summary
events, file paths). Zod-validated query (q 1-200 chars, types csv, limit 1-60),
grouped session->event->file with exact-match-first + recency tiebreak, total
cap 60 + per-group cap 25, snippet cap 200, path-safety (relativePath only).
Frontend search box (history panel) deferred to next cycle; resume/history-prompt
text matching deferred to v1.1 (lives in large on-disk files, out of v1 bounded scope).

New: src/search-service.ts (pure core), src/types/search.ts, src/web/routes/search-routes.ts.
Tests: test/search-service.test.ts (14), test/routes/search-routes.test.ts (10).

src/web/server.ts

@@ -149,6 +149,7 @@ import {
   registerRalphRoutes,
   registerPlanRoutes,
   registerClipboardRoutes,
+  registerSearchRoutes,
   registerOrchestratorRoutes,
   registerWsRoutes,
 } from './routes/index.js';
@@ -869,6 +870,7 @@ export class WebServer extends EventEmitter {
     registerRalphRoutes(this.app, ctx);
     registerPlanRoutes(this.app, ctx);
     registerClipboardRoutes(this.app, ctx);
+    registerSearchRoutes(this.app, ctx);
     registerOrchestratorRoutes(this.app, ctx);
     registerWsRoutes(this.app, ctx, () => this.getHostPolicy());
   }