Sentry wired up, tests everywhere

Observability and housekeeping

• Integrated Sentry for production error tracking and merged it (PR #315). Wired up client/server/edge, enabled source maps via withSentryConfig, added a /monitoring tunnel, and routed error boundaries through captureException.
• Tightened privacy and noise: scrubbed PII (email, journal content) in beforeSend/beforeBreadcrumb, disabled locally, and filtered expected 401/403s. Also updated CSP connect-src for Sentry ingest.
• Dropped in Dependabot config and CODEOWNERS to keep things tidy.

Testing and hardening

• Big coverage push across the app: added page-level snapshots/action tests for previously untested pages/layouts plus a sweep over settings, integration sub-components, onboarding, journals, middleware, i18n, manifest/robots, and OG image utils. Ended at 123 test files, 848 tests, all green.
• Killed a date-based flake by freezing time in a snapshot test (vi.useFakeTimers). Also bumped a snapshot for the March 1 → 2 rollover to keep CI calm.
• Patched tests for Node 22 by stubbing localStorage/sessionStorage (fixed token and theme tests). Corrected a few API expectation mismatches in journal tests (DELETE for unpublish, regenerate/status paths).
• Fixed a subtle markdown excerpt bug by stripping images before links so images don’t leak into summaries (commit).