feat: add changelog and versioning, surface it in admin

Bumps version to 0.2.0 (root + apps/web package.json) and adds
CHANGELOG.md as the canonical human-readable history, mirrored by
apps/web/lib/changelog.ts as the in-app data source (single
ChangelogList component renders both).

- /changelog: user-facing page, linked from the account dropdown.
- /admin/changelog: same list, plus a "Version" card on the admin
  overview dashboard linking to it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/messages/en.json

@@ -11,6 +11,7 @@
     "pantry": "Pantry",
     "shopping": "Shopping",
     "settings": "Settings",
+    "changelog": "Changelog",
     "admin": "Admin",
     "signOut": "Sign out",
     "apiKeys": "API keys",