feat: Support standard gitignore syntax with pathspec library

[CodeMaverick-143]

Feature Request

Replace naive folder matching in insight/utils.py with standard Git ignore pattern matching using pathspec.

Problem with Current Implementation

Currently, get_ignored_dirs() only matches exact top-level directory names. It cannot handle:

• Standard glob patterns (e.g., *.min.js, *.log, tests/**)
• File path patterns (e.g., src/generated/*)
• Negation patterns (e.g., !important.py)

Proposed Solution

1. Add pathspec to requirements.txt and setup.py.
2. Load patterns from .gitignore and .insightignore.
3. Use pathspec.PathSpec.from_lines("gitwildmatch", patterns) to filter discovered files and directories.