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/unit/test_config.py

@@ -1,5 +1,3 @@
-import os
-import pytest
 
 
 _BASE_ENV = {
@@ -26,6 +24,7 @@ def test_settings_load_from_env(monkeypatch):
 
     # Import inside test to pick up monkeypatched env
     import importlib
+
     import app.config as config_module
     importlib.reload(config_module)
 
@@ -42,6 +41,7 @@ def test_settings_max_upload_bytes_override(monkeypatch):
     _apply_env(monkeypatch, {"MAX_UPLOAD_BYTES": "10485760"})
 
     import importlib
+
     import app.config as config_module
     importlib.reload(config_module)
 
@@ -53,6 +53,7 @@ def test_settings_jwt_expiry_override(monkeypatch):
     _apply_env(monkeypatch, {"JWT_EXPIRY_SECONDS": "3600"})
 
     import importlib
+
     import app.config as config_module
     importlib.reload(config_module)