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_delete.py

@@ -44,7 +44,6 @@ async def test_delete_removes_storage_object(client):
     )
     assert upload.status_code in (200, 201)
     image_id = upload.json()["id"]
-    storage_key = upload.json()["hash"]
 
     delete_resp = await client.delete(f"/api/v1/images/{image_id}")
     assert delete_resp.status_code == 204