Feat: Add tag browser page at /tags with count-sorted tag list and library deep-link

- Extends GET /api/v1/tags with sort=count_desc and min_count query params
- New TagsComponent at /tags (public, no auth guard) shows all tags sorted by image count
- Clicking a tag navigates to /?tags=<name> for a pre-filtered library view
- LibraryComponent reads ?tags= query param on init to support deep-linking from tag browser
- Library header gains a "Browse tags" link to /tags for discoverability
- All 15 TDD tasks complete; ruff, ng lint, and ng build clean

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/tests/integration/test_upload.py

@@ -79,6 +79,7 @@ async def test_upload_invalid_mime_type_returns_422(client):
 @pytest.mark.asyncio
 async def test_upload_oversized_file_returns_422(client):
     import os
+
     from app.config import get_settings
 
     os.environ["MAX_UPLOAD_BYTES"] = "10"