[NOTIF-001] Connect notification inbox to stored notifications

[chev0004]

Outline

Summary

Connects the notification inbox to per-user stored notifications, so a logged-in user sees their real notifications instead of an empty placeholder, with read, delete, and clear actions persisted server-side.

---

Changes & Enhancements

• Type of Change:
  • Feature
  • Bugfix
  • Refactor
  • Chore
• Changes:
  • (database):
    • Add a notifications table with a notification_kind enum, per-user indexes, and migration 0008.
  • (data layer):
    • Add notification queries: list, create, mark read, mark all read, delete, and clear.
  • (api):
    • Add /api/notifications for fetching the current user's notifications and persisting read, delete, and clear actions.
  • (inbox):
    • Load notifications from storage on open and persist every action, deriving relative timestamps and the unread count from server state.
  • (discovery, public profile):
    • Create a notification for a profile owner when a logged-in user copies their username.

---

Page / App Changes

Affected Next.js Routes (Local):

• /[lang], /[lang]/profile, /[lang]/saved, /[lang]/u/[id] (navbar inbox now loads stored notifications)
• /api/notifications (new route handler for fetch, mutate, and create)

Before (Screenshot)

After (Screenshot)

---

Component / Storybook Changes

Affected Storybook Components (Local):

• Components > Inbox > Free Notifications
• Components > Inbox > Empty

Before (Screenshot)

After (Screenshot)

---

Not Doing

• Only the username-copy action emits notifications; other triggers such as profile views can reuse the same creation path later.

---

Other (Remarks)

---

Checklists

• Code is well-documented (comments, JSDoc, etc.).
• Existing comments were updated as needed.
• No out-of-scope changes are included.
• Write TODO comments where future work is required.
• Removed unnecessary debug code (e.g., console.log, debugger).
• Self-reviewed and tested locally.