chore(repo): restructure as monorepo with server and client workspaces

- move NestJS app into server/ subdirectory
- add client/ React+TypeScript (Vite) app with Hello World
- update docker-compose to build and run both services
- add root package.json declaring npm workspaces
- update .gitignore to cover node_modules and dist at all depths

server/src/session/session-scheduler.service.ts

@@ -0,0 +1,53 @@
+import { Injectable } from "@nestjs/common";
+import { Interval } from "@nestjs/schedule";
+import { ConfigService } from "@nestjs/config";
+import { AppConfig } from "../config/app.config";
+import { TraceLogger } from "../common/trace-logger";
+import { SessionService } from "./session.service";
+import { SessionContextService } from "./session-context.service";
+
+/**
+ * Periodically:
+ *  1. Closes sessions that have been idle for longer than SESSION_IDLE_TIMEOUT_MINUTES.
+ *  2. Deletes closed sessions whose updatedAt is older than SESSION_DELETE_CLOSED_DAYS.
+ */
+@Injectable()
+export class SessionSchedulerService {
+  private readonly logger = new TraceLogger(SessionSchedulerService.name);
+
+  constructor(
+    private readonly sessionService: SessionService,
+    private readonly sessionContextService: SessionContextService,
+    private readonly config: ConfigService<AppConfig, true>,
+  ) {}
+
+  @Interval(60_000)
+  async runScheduler(): Promise<void> {
+    await this.closeExpired();
+    await this.deleteOldClosed();
+  }
+
+  private async closeExpired(): Promise<void> {
+    const idleMinutes = this.config.get("SESSION_IDLE_TIMEOUT_MINUTES");
+    const cutoff = new Date(Date.now() - idleMinutes * 60_000);
+    const expired = await this.sessionService.findExpiredOpen(cutoff);
+    for (const session of expired) {
+      await this.sessionContextService.close(session.sessionName);
+      this.logger.log(
+        `Session "${session.sessionName}" closed (idle > ${idleMinutes} min)`,
+      );
+    }
+  }
+
+  private async deleteOldClosed(): Promise<void> {
+    const days = this.config.get("SESSION_DELETE_CLOSED_DAYS");
+    const cutoff = new Date(Date.now() - days * 86_400_000);
+    const old = await this.sessionService.findOldClosed(cutoff);
+    for (const session of old) {
+      await this.sessionService.remove(session.id);
+      this.logger.log(
+        `Session "${session.sessionName}" deleted (closed > ${days} days ago)`,
+      );
+    }
+  }
+}