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_config.py

@@ -1,16 +1,19 @@
 """
 Unit tests for config.py - IP parsing, environment validation.
 """
-import pytest
+
 from unittest.mock import Mock
+
+import pytest
+
 from config import (
-    _parse_ip,
     _ip_matches_ranges,
+    _parse_ip,
+    get_client_ip,
+    get_forwarded_client_ip,
     is_lan_ip,
     is_tailscale_ip,
     is_trusted_proxy,
-    get_forwarded_client_ip,
-    get_client_ip,
 )
 
 
@@ -146,15 +149,15 @@ class TestIsTailscaleIP:
     def test_is_tailscale_ip_invalid(self):
         """Test non-Tailscale IPs."""
         assert not is_tailscale_ip("100.63.255.255")  # Just below range
-        assert not is_tailscale_ip("100.128.0.0")     # Just above range
+        assert not is_tailscale_ip("100.128.0.0")  # Just above range
         assert not is_tailscale_ip("192.168.1.1")
         assert not is_tailscale_ip("10.0.0.1")
 
     def test_is_tailscale_ip_boundary(self):
         """Test Tailscale IP range boundaries."""
         # 100.64.0.0/10 means 100.64.0.0 to 100.127.255.255
-        assert is_tailscale_ip("100.64.0.0")      # Start of range
-        assert is_tailscale_ip("100.127.255.255") # End of range
+        assert is_tailscale_ip("100.64.0.0")  # Start of range
+        assert is_tailscale_ip("100.127.255.255")  # End of range
 
 
 class TestIsTrustedProxy:
@@ -283,8 +286,10 @@ class TestConfigValidation:
         monkeypatch.setenv("SECRET_KEY", "short")
 
         with pytest.raises(RuntimeError, match="SECRET_KEY must be set and at least 32 characters"):
-            import config
             import importlib
+
+            import config
+
             importlib.reload(config)
 
     def test_secret_key_empty(self, monkeypatch):
@@ -292,6 +297,8 @@ class TestConfigValidation:
         monkeypatch.delenv("SECRET_KEY", raising=False)
 
         with pytest.raises(RuntimeError, match="SECRET_KEY must be set and at least 32 characters"):
-            import config
             import importlib
+
+            import config
+
             importlib.reload(config)