fix: resolve stale realtime updates and cache invalidation

[web3dev1337]

Summary

• invalidate stale backend caches on mutation events before broadcasting websocket updates
• reduce dynamic cache TTLs for status/agents/rigs/convoys to improve freshness
• add frontend forced-refresh pathways (refresh=true) for status/mail/agents/rigs/crews
• add debounced realtime refresh scheduling with focus/visibility refresh, queued trailing refresh, and reduced background refresh overhead
• add real-server integration coverage for cache invalidation after rig/service mutations
• update CODEBASE_DOCUMENTATION.md for new integration test coverage

Validation

• npm install
• npm run lint (fails: no lint script in package)
• npm run build (fails: no build script in package)
• npm test (39 files, 327 tests)
• npm run test:e2e (1 file, 27 tests)
• headless Puppeteer smoke against test/mock-server.js (no page/console/network errors)

Closes #21