feat(ui): add include submodules toggle to web interface

[samarthsaxena2004]

🚀 Description

This PR implements the requested feature to allow users to toggle Git submodule inclusion directly from the web interface. While the capability existed in the core engine and CLI, it was previously inaccessible to Web UI users.

🛠️ Changes Made

• Frontend: Added a custom-styled checkbox for "Include Submodules" in git_form.jinja.
• JavaScript: Updated collectFormData in utils.js to capture and send the state of the new checkbox.
• API Models: Updated IngestRequest in models.py to include and document the include_submodules boolean field.
• Plumbing: Modified api_ingest, _perform_ingestion, and process_query to use keyword-only arguments for boolean flags and ensured the documentation (docstrings) meets project standards.

✅ Testing Performed

• Pre-commit Integrity: Verified that all ruff and pydoclint hooks pass successfully.
• UI Verification: Confirmed the toggle appears correctly on 127.0.0.1:8000.
• End-to-End: Ingested a repository containing submodules and verified that submodule contents are recursively updated and included in the output tree.

🔗 Related Issues

Closes #554