fix(processing): add per-step timeout enforcement to gracefulshutdown

[beulah7717108-eng]

Summary

Adds per-step timeout enforcement to GracefulShutdown so no single hanging hook can block the entire shutdown sequence. Each registered shutdown hook now accepts an optional timeoutMs override. If a step exceeds its timeout, a warning is logged and shutdown continues to the next step. drainAll() in SessionRegistry also respects a per-session drain timeout via the SESSION_DRAIN_TIMEOUT_MS env var.

Also adds SHUTDOWN_TIMEOUT_MS and SESSION_DRAIN_TIMEOUT_MS to the config Zod schema so these values are validated at startup rather than read raw from process.env.

Related issues

Closes #342

Type of change

• fix

Testing performed

cd xstreamroll-processing
npx tsc --noEmit                          # 0 errors
npx jest --testPathPattern='(lifecycle.shutdown|session-registry|lifecycle)\.test\.ts' --no-coverage
                                          # 32 passed, 0 failures

Tests added:

• lifecycle.shutdown.test.ts: 4 new tests covering per-step timeout (hook exceeds timeout, per-step override, fallback to global timeout, multiple timed-out hooks)
• session-registry.test.ts: 1 new test for drainAll() with timeout when a session's stop() hangs forever

Checklist — author

• I rebased onto origin/main and resolved conflicts.
• I ran the quality gates locally: npm run lint, npm run build, npm test.
• Title follows Conventional Commits and references the issue (see above).
• I added/updated tests where applicable and they pass locally.
• No new TypeScript errors or lint warnings introduced.
• Screenshots included for UI changes.