feat: hot-reloaded runtime config (src/lib/runtime-config.ts), greeting on GET /, GET /admin/runtime-config

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app.ts

@@ -6,6 +6,11 @@ import type { Config } from "./lib/config.js";
 import type { Db } from "./lib/db.js";
 import type { Flags } from "./lib/flags.js";
 import type { Cache } from "./lib/redis.js";
+import {
+  staticRuntimeConfig,
+  type RuntimeConfig,
+} from "./lib/runtime-config.js";
+import { adminRouter } from "./routes/admin.js";
 import { healthRouter } from "./routes/health.js";
 import { logDemoRouter } from "./routes/log-demo.js";
 import { rootRouter } from "./routes/root.js";
@@ -16,9 +21,17 @@ export interface Deps {
   db?: Db;
   cache?: Cache;
   flags?: Flags;
+  runtimeConfig?: RuntimeConfig;
 }
 
-export function createApp({ config, logger, db, cache, flags }: Deps) {
+export function createApp({
+  config,
+  logger,
+  db,
+  cache,
+  flags,
+  runtimeConfig = staticRuntimeConfig(),
+}: Deps) {
   const app = express();
   app.disable("x-powered-by");
 
@@ -45,7 +58,8 @@ export function createApp({ config, logger, db, cache, flags }: Deps) {
   );
 
   app.use(healthRouter({ db, cache }));
-  app.use(rootRouter({ config, db, cache, flags }));
+  app.use(rootRouter({ config, db, cache, flags, runtimeConfig }));
+  app.use(adminRouter({ runtimeConfig }));
   app.use(logDemoRouter());
 
   // Express identifies error handlers by arity; keep all four args.