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/README-PRECOMMIT.md

@@ -0,0 +1,85 @@
+# Pre-commit Hooks Setup
+
+This project uses pre-commit hooks to ensure code quality before commits.
+
+## Tools
+
+- **black**: Code formatter (line length: 120)
+- **ruff**: Fast Python linter
+- **pre-commit-hooks**: Basic file checks (trailing whitespace, YAML validation, etc.)
+
+## Installation
+
+### Option 1: Manual Installation (Recommended for this repo)
+
+Since this repo has a custom `core.hooksPath`, install pre-commit manually:
+
+```bash
+cd dashboard/backend
+source venv/bin/activate
+pip install -r requirements-dev.txt
+
+# Run manually before committing
+pre-commit run --all-files
+```
+
+### Option 2: Standard Installation
+
+If you want to use pre-commit's automatic hooks:
+
+```bash
+cd /path/to/nas-tools
+git config --unset-all core.hooksPath
+cd dashboard/backend
+source venv/bin/activate
+pre-commit install
+```
+
+## Usage
+
+### Run on all files
+```bash
+cd dashboard/backend
+source venv/bin/activate
+pre-commit run --all-files
+```
+
+### Run on staged files only
+```bash
+pre-commit run
+```
+
+### Run specific hook
+```bash
+pre-commit run black --all-files
+pre-commit run ruff --all-files
+```
+
+### Skip hooks (not recommended)
+```bash
+git commit --no-verify
+```
+
+## Configuration
+
+- `.pre-commit-config.yaml`: Hook configuration
+- `pyproject.toml`: Black and Ruff settings
+
+## What the hooks check
+
+1. **black**: Formats Python code to consistent style
+2. **ruff**: Checks for common Python errors and style issues
+3. **trailing-whitespace**: Removes trailing whitespace
+4. **end-of-file-fixer**: Ensures files end with newline
+5. **check-yaml**: Validates YAML syntax
+6. **check-json**: Validates JSON syntax
+7. **check-merge-conflict**: Detects merge conflict markers
+8. **check-added-large-files**: Prevents committing large files (>1MB)
+
+## CI Integration
+
+The test workflow runs these checks automatically:
+- Tests must pass
+- Coverage must be ≥50%
+
+Pre-commit hooks help catch issues locally before pushing to CI.