Implement file watching infrastructure for auto-reload

[krystophny]

Problem

The test suite expects file watching capabilities for configuration reload and incremental analysis, but the infrastructure doesn't exist.

Missing Components

• file_watcher_t type
• File system monitoring
• Change detection and callbacks
• Configuration auto-reload on changes

Test Failures

• test_file_watching - RED phase (0% passing)
• test_configuration_reload - Partially affected

Requirements

1. Watch .toml configuration files
2. Watch source files for incremental analysis
3. Platform-independent implementation (Linux/Mac/Windows)
4. Efficient - don't poll, use OS notifications where possible

Proposed Implementation

type :: file_watcher_t
    \! Track watched files and callbacks
contains
    procedure :: watch_file
    procedure :: watch_directory  
    procedure :: stop_watching
    procedure :: check_changes  \! For polling fallback
end type

Priority

High - Essential for IDE integration and developer experience

Related Issues

• Implement incremental analysis and intelligent caching #17 (incremental analysis needs file watching)
• Configuration hot-reload feature