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>

services/issue_service.py

@@ -35,8 +35,8 @@ class IssueService:
 
     def create_enhancement_issue(self, title: str, use_case: str,
                                technical_requirements: str = "",
-                               acceptance_criteria: List[str] = None,
-                               dependencies: List[str] = None,
+                               acceptance_criteria: Optional[List[str]] = None,
+                               dependencies: Optional[List[str]] = None,
                                priority: str = "Medium") -> Dict[str, Any]:
         """Create a structured enhancement issue."""
         return self.issue_creator.create_enhancement_issue(

services/project_service.py

@@ -2,7 +2,7 @@
 Project service - business logic for project management operations.
 """
 
-from typing import List, Dict, Any
+from typing import List, Dict, Any, Optional
 
 from tddai.project_manager import ProjectManager, ProjectState, Priority, Milestone, Label
 from tddai import TddaiError
@@ -18,7 +18,7 @@ class ProjectService:
         """Setup project management labels and structure."""
         self.project_manager.ensure_project_labels()
 
-    def create_milestone(self, title: str, description: str = "", due_date: str = None) -> Milestone:
+    def create_milestone(self, title: str, description: str = "", due_date: Optional[str] = None) -> Milestone:
         """Create a new milestone (project)."""
         return self.project_manager.create_milestone(title, description, due_date)