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>

tddai_cli.py

@@ -9,6 +9,7 @@ Business logic is handled by services, presentation by CLI framework.
 import sys
 import argparse
 from pathlib import Path
+from typing import Optional, Any
 
 # Add current directory to path so we can import modules
 sys.path.insert(0, str(Path(__file__).parent))
@@ -16,9 +17,9 @@ sys.path.insert(0, str(Path(__file__).parent))
 from cli import CLIFramework
 
 # Lazy initialization of CLI framework
-_cli_framework = None
+_cli_framework: Optional[CLIFramework] = None
 
-def _get_cli():
+def _get_cli() -> CLIFramework:
     """Get CLI framework instance (lazy initialization)."""
     global _cli_framework
     if _cli_framework is None:
@@ -26,49 +27,49 @@ def _get_cli():
     return _cli_framework
 
 
-def workspace_status():
+def workspace_status() -> None:
     """Show current workspace status."""
     _get_cli().workspace_status()
 
 
-def start_issue(issue_number: int):
+def start_issue(issue_number: int) -> None:
     """Start working on an issue."""
     _get_cli().start_issue(issue_number)
 
 
-def finish_issue():
+def finish_issue() -> None:
     """Finish current issue workspace."""
     _get_cli().finish_issue()
 
 
-def add_test_guidance():
+def add_test_guidance() -> None:
     """Show guidance for adding tests."""
     _get_cli().add_test_guidance()
 
 
-def list_issues():
+def list_issues() -> None:
     """List all issues."""
     _get_cli().list_issues()
 
 
-def list_open_issues():
+def list_open_issues() -> None:
     """List only open issues."""
     _get_cli().list_open_issues()
 
 
-def show_issue(issue_number: int):
+def show_issue(issue_number: int) -> None:
     """Show detailed issue information."""
     _get_cli().show_issue(issue_number)
 
 
-def create_issue(title: str, body: str, issue_type: str = "enhancement"):
+def create_issue(title: str, body: str, issue_type: str = "enhancement") -> None:
     """Create a new issue."""
     _get_cli().create_issue(title, body, issue_type)
 
 
 def create_enhancement_issue(title: str, use_case: str, technical_requirements: str = "",
                            acceptance_criteria: str = "", dependencies: str = "",
-                           priority: str = "Medium"):
+                           priority: str = "Medium") -> None:
     """Create a structured enhancement issue."""
     # Parse acceptance criteria if provided
     criteria_list = []
@@ -90,52 +91,52 @@ def create_enhancement_issue(title: str, use_case: str, technical_requirements:
     )
 
 
-def create_from_template(template_file: str, **kwargs):
+def create_from_template(template_file: str, **kwargs: Any) -> None:
     """Create issue from template file."""
     _get_cli().create_from_template(template_file, **kwargs)
 
 
-def analyze_coverage(issue_number: int):
+def analyze_coverage(issue_number: int) -> None:
     """Analyze test coverage for a specific issue."""
     _get_cli().analyze_coverage(issue_number)
 
 
-def setup_project_management():
+def setup_project_management() -> None:
     """Setup project management labels and milestones."""
     _get_cli().setup_project_management()
 
 
-def move_issue_to_state(issue_number: int, state: str):
+def move_issue_to_state(issue_number: int, state: str) -> None:
     """Move issue to a specific project state."""
     _get_cli().move_issue_to_state(issue_number, state)
 
 
-def set_issue_priority(issue_number: int, priority: str):
+def set_issue_priority(issue_number: int, priority: str) -> None:
     """Set issue priority."""
     _get_cli().set_issue_priority(issue_number, priority)
 
 
-def create_milestone(title: str, description: str = ""):
+def create_milestone(title: str, description: str = "") -> None:
     """Create a new milestone (project)."""
     _get_cli().create_milestone(title, description)
 
 
-def list_milestones():
+def list_milestones() -> None:
     """List all milestones."""
     _get_cli().list_milestones()
 
 
-def assign_issue_to_milestone(issue_number: int, milestone_id: int):
+def assign_issue_to_milestone(issue_number: int, milestone_id: int) -> None:
     """Assign issue to a milestone."""
     _get_cli().assign_issue_to_milestone(issue_number, milestone_id)
 
 
-def project_overview():
+def project_overview() -> None:
     """Show project management overview."""
     _get_cli().project_overview()
 
 
-def issue_index(format_type="tsv", sort_by="number", filter_state=None, filter_priority=None, include_state=False):
+def issue_index(format_type: str = "tsv", sort_by: str = "number", filter_state: Optional[str] = None, filter_priority: Optional[str] = None, include_state: bool = False) -> None:
     """Output compact index of all issues for Unix processing."""
     _get_cli().issue_index(
         format_type=format_type,
@@ -146,7 +147,7 @@ def issue_index(format_type="tsv", sort_by="number", filter_state=None, filter_p
     )
 
 
-def main():
+def main() -> None:
     """Main CLI entry point."""
     parser = argparse.ArgumentParser(description="tddai CLI tool")
     subparsers = parser.add_subparsers(dest='command', help='Available commands')