feat(app): add private Session notifications

[ctwhome]

Summary

• Projects exactly-once durable attention records from completion, pending approval, pending clarification, failure, and unknown-delivery semantic events.
• Adds an accessible in-app attention center, unread badge, foreground suppression, explicit permission/settings flow, optional foreground sound, and exact Project/Session deep links.
• Adds private endpoint management and optional Web Push with encrypted-at-rest subscription credentials, private DB/key permissions, restart-safe retry scheduling, endpoint baselines, expired-subscription handling, and generic redacted payloads.
• Extends the PWA service worker for safe push display/click/close handling and durable acted/read acknowledgement.
• Keeps canonical notifications available when system notifications are unavailable and never grants approval or submits clarification from a lock screen.

Security and privacy

• Push endpoint, p256dh, and auth values are AES-256-GCM encrypted with a local 0600 key; DB directory/file/key modes are repaired to 0700/0600/0600.
• APIs expose device metadata only and mutations require exact same origin.
• Payloads contain generic copy plus canonical identifiers/deep links—never prompts, transcript, Project/Session titles, paths, tool arguments, answers, or secret-bearing errors.
• New or re-enabled endpoints never replay historical/read/dismissed/acted/resolved notifications.

Verification

• bun test — 389 passed, 4 opt-in integrations skipped
• bun run --cwd app check — 0 errors, 0 warnings
• production build/service worker — passed
• HUE_E2E_PORT=4493 bun run --cwd app test:e2e — 55 passed
• focused notification suites after final click sequencing repair — 8 passed
• changed-file Prettier and git diff --check — passed
• independent security/correctness review — CLEAN after four server/privacy repairs and foreground-click behavioral test repair

Device evidence

Browser integration is verified. Closed installed-PWA Web Push, Android notification-channel behavior, and Wear OS mirroring remain real-device/emulator evidence and continue in #86; no physical-device claim is made here.

Stack

Depends on #89, which depends on #87. Merge in that order, then retarget/reverify each stacked PR.

Closes #84