Closes #410

• Add support for linting specific files and directories via arguments
• Implement smart file type detection (Python, YAML, JSON, Markdown, TOML)
• Add convenience targets: lint-quick, lint-fix, lint-smart
• Add git integration: lint-changed, lint-staged, pre-commit hooks
• Fix TARGET variable parsing for multiple directories
• Add dummy targets to prevent 'No rule to make target' errors

✅ Changes Made

Core Implementation

• Fixed TARGET variable handling: Changed from TARGET ?= mcpgateway tests to DEFAULT_TARGETS := mcpgateway tests; TARGET ?= $(DEFAULT_TARGETS) to properly handle multiple directories
• Added dummy target support: Implemented ifneq block to create dummy targets for file arguments, preventing "No rule to make target" errors
• Enhanced argument parsing: Updated lint target to properly handle multiple file arguments passed as additional goals

Linting Enhancements

• Smart file type detection: Added lint-smart target that auto-detects file types (.py, .yaml, .json, .md, .toml, .sh) and runs appropriate linters
• File-specific linting targets: Implemented lint-py, lint-yaml, lint-json, lint-md for targeting specific file types
• Convenience targets: Added lint-quick (fast linters only), lint-fix (auto-fix formatting), lint-changed (git integration)

Git Integration

• Changed files linting: make lint-changed lints only files modified in git
• Staged files linting: make lint-staged lints only git-staged files
• Pre-commit hook support: Added targets for git hook integration

🚀 Usage Examples

# Single file linting
make lint mcpgateway/config.py

# Directory linting  
make lint mcpgateway/

# Multiple files
make lint mcpgateway/config.py mcpgateway/validators.py

# Quick lint (fast checks only)
make lint-quick mcpgateway/config.py

# Auto-fix formatting issues
make lint-fix mcpgateway/config.py

# Smart file type detection
make lint-smart config.yaml

# Git integration
make lint-changed    # Lint only changed files
make lint-staged     # Lint only staged files

# Traditional full project (still works)
make lint

✅ Acceptance Criteria Met

• ✅ make lint filename works for single files
• ✅ make lint dirname works for directories
• ✅ make lint without args still lints entire project
• ✅ All Python linters support file/directory targeting
• ✅ Config file linters detect file type and run appropriately
• ✅ Clear error messages for non-existent files
• ✅ make lint-fix repairs formatting issues
• ✅ make lint-quick provides fast feedback
• ✅ Performance: Single file linting is notably faster than full project
• ✅ Git integration for changed/staged files
• ✅ Pre-commit hook support

🧪 Testing

All functionality has been tested and verified:

# Core functionality tests
make lint mcpgateway/config.py          # ✅ Single file
make lint mcpgateway/                   # ✅ Directory  
make lint                               # ✅ Full project
make lint-quick mcpgateway/config.py    # ✅ Quick lint
make lint-fix mcpgateway/config.py      # ✅ Auto-fix
make lint-changed                       # ✅ Git integration

# File type detection tests  
make lint-smart test.yaml               # ✅ YAML detection
make lint-smart test.json               # ✅ JSON detection
make lint-smart test.md                 # ✅ Markdown detection

# Error handling tests
make lint nonexistent.py               # ✅ Graceful error for missing files