feat: multi-location task inject with new file creation

[melihemik]

Multi-Location Task Inject & File Creation Support

Summary of Changes:

• Multi-Location Injections: Inject tasks into multiple files/lines simultaneously in a single commit & PR.
• New File Creation: Support for creating new files directly during task injection with clean comment formatting.
• Per-Location Descriptions: Distinct notes/descriptions for each injected file/line.
• Structured PR Descriptions: Automatic markdown table breakdown in generated PRs detailing all created/modified files, lines, and task annotations.
• UI Enhancements: Modernized TaskInjector slide-out panel with location management (add/remove/new file toggle) and refined task cards on the board.

Verified with go test ./... and npm run build.