[PROFILE-003] Add public profile route and card actions

[chev0004]

Outline

Summary

Adds locale-aware public profile pages and wires the discovery card and profile editor actions to real routes and share behavior.

---

Changes & Enhancements

• Type of Change:
  • Feature
  • Bugfix
  • Refactor
  • Chore
• Changes:
  • (public profile):
    • Add /[lang]/u/[id] route rendering public profile data, returning 404 for missing or non-public profiles.
  • (discovery):
    • Wire card "View profile" to the public route and "Share profile" to the real public URL with clipboard fallback and toasts.
    • Tag, language, and country clicks now add the matching discovery filter.
  • (profile editor):
    • Wire "View public profile" to the current user's public route when their profile is public.
  • (inbox):
    • Reset notification state from a content signature instead of the array reference, fixing a "Maximum update depth exceeded" loop when the notifications prop is a fresh array each render.

---

Page / App Changes

Affected Next.js Routes (Local):

• /[lang]/u/[id] (new)
• /[lang] (discovery card actions)
• /[lang]/profile (editor menu link)

Before (Screenshot)

After (Screenshot)

---

Component / Storybook Changes

Affected Storybook Components (Local):

Before (Screenshot)

After (Screenshot)

---

Not Doing

---

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.