feat: comprehensive test infrastructure improvements

- Fix unit test imports: add env setup in conftest.py before module imports
- Add 24 new auth router tests (RBAC, preferences, password validation)
- Add 16 new tests for litellm and chat_summary routers
- Apply black formatting and ruff linting across codebase
- Add pre-commit hooks configuration (black, ruff, file checks)
- Increase CI coverage threshold from 40% to 50%

Test Results:
- 206 tests passing (91 unit + 115 integration)
- Coverage: 58.79% on core modules
- auth.py: 57% → 85%, litellm.py: 23% → 87%, chat_summary.py: 41% → 100%
- auth_service: 96.51%, config: 100%, rbac: 93.48%

dashboard/backend/tests/unit/test_rbac.py

@@ -1,19 +1,20 @@
 """
 Unit tests for rbac.py - Role-based access control.
 """
-import pytest
+
 import json
 import os
+
 from rbac import (
-    load_rbac,
-    save_rbac,
-    update_rbac,
-    resolve_role,
+    DEFAULT_RBAC,
+    ROLE_GROUP_MAP,
     get_pages,
     get_sidebar_links,
     get_sidebar_order,
-    DEFAULT_RBAC,
-    ROLE_GROUP_MAP,
+    load_rbac,
+    resolve_role,
+    save_rbac,
+    update_rbac,
 )
 
 
@@ -58,7 +59,7 @@ class TestSaveRBAC:
         rbac_file = os.path.join(temp_volume_root, "docker/nas-dashboard/rbac.json")
         test_data = {
             "role_defaults": {"admin": {"pages": "*"}},
-            "user_overrides": {"testuser": {"pages": ["dashboard"]}}
+            "user_overrides": {"testuser": {"pages": ["dashboard"]}},
         }
 
         save_rbac(test_data)
@@ -74,6 +75,7 @@ class TestSaveRBAC:
 
         # Remove directory
         import shutil
+
         if os.path.exists(os.path.dirname(rbac_file)):
             shutil.rmtree(os.path.dirname(rbac_file))
 
@@ -88,6 +90,7 @@ class TestUpdateRBAC:
 
     def test_update_rbac_with_mutator(self, mock_config, temp_rbac_file):
         """Test updating RBAC with mutator function."""
+
         def add_user_override(data):
             data["user_overrides"]["newuser"] = {"pages": ["dashboard", "docker"]}
             return "success"
@@ -188,6 +191,7 @@ class TestGetPages:
 
     def test_get_pages_with_user_override(self, mock_config, temp_rbac_file):
         """Test getting pages with user-specific override."""
+
         # Add user override
         def add_override(data):
             data["user_overrides"]["customuser"] = {"pages": ["dashboard", "files"]}
@@ -223,11 +227,9 @@ class TestGetSidebarLinks:
 
     def test_get_sidebar_links_with_user_override(self, mock_config, temp_rbac_file):
         """Test getting sidebar links with user override."""
+
         def add_override(data):
-            data["user_overrides"]["customuser"] = {
-                "pages": "*",
-                "sidebar_links": ["dashboard", "docker", "files"]
-            }
+            data["user_overrides"]["customuser"] = {"pages": "*", "sidebar_links": ["dashboard", "docker", "files"]}
 
         update_rbac(add_override)
 
@@ -236,6 +238,7 @@ class TestGetSidebarLinks:
 
     def test_get_sidebar_links_no_override(self, mock_config, temp_rbac_file):
         """Test that user without sidebar_links override gets role default."""
+
         def add_override(data):
             data["user_overrides"]["customuser"] = {"pages": ["dashboard"]}
             # No sidebar_links specified
@@ -256,10 +259,7 @@ class TestGetSidebarOrder:
 
     def test_get_sidebar_order_with_override(self, mock_config, temp_rbac_file):
         """Test getting sidebar order with user override."""
-        custom_order = {
-            "Main": ["dashboard", "docker"],
-            "Media": ["navidrome", "immich"]
-        }
+        custom_order = {"Main": ["dashboard", "docker"], "Media": ["navidrome", "immich"]}
 
         def add_override(data):
             data["user_overrides"]["customuser"] = {"sidebar_order": custom_order}