feat: Complete type safety improvements for CLI and service layers

Implement comprehensive type annotations and mypy configuration as part
of code quality initiative. Achieve 100% type annotation coverage for
main CLI entry points and resolve Optional type inconsistencies.

## Key Improvements

### CLI Layer (100% Type Coverage)
- tddai_cli.py: Complete type annotations for all 21 functions
- cli/core.py: Full type coverage for CLI framework (20 functions)
- cli/commands/issues.py: Fixed Optional[List[str]] parameter types
- cli/commands/workspace.py: Improved type checker logic for Optional handling

### Service Layer Type Safety
- services/issue_service.py: Fixed Optional parameter type signatures
- services/project_service.py: Updated Optional type annotations
- tddai/issue_creator.py: Proper Optional[List[str]] usage
- tddai/project_manager.py: Fixed Optional parameter handling

### Mypy Configuration
- pyproject.toml: Added comprehensive mypy configuration
- Gradual adoption strategy with module-specific strictness
- Python 3.12 compatibility for proper type checking
- Incremental typing approach for legacy modules

## Technical Details
- Proper Optional vs Union type usage throughout
- Generic type annotations for collections
- Return type annotations for all public functions
- Fixed implicit Optional violations (PEP 484)
- Type checker logic improvements for better safety

## Benefits
- Improved IDE autocomplete and error detection
- Compile-time type checking for CLI commands
- Better maintainability and debugging capabilities
- Foundation for expanding type safety to remaining modules

Resolves #27 - Type safety improvements

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

cli/commands/workspace.py

@@ -47,6 +47,7 @@ class WorkspaceCommands:
                 OutputFormatter.error("No active issue workspace")
                 print("   Nothing to finish")
                 OutputFormatter.exit_with_error("", 1)
+                return  # Explicit return for type checker
 
             # Get test count before finishing
             summary = self.service.get_workspace_summary()