[Feature] : Add Recycle Bin (Trash / Restore Flow)

[hrshjswniii]

🔗 Related Issue

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Closes #541

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📝 What does this PR do?

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This PR implements a dedicated Recycle Bin (Trash / Restore) workflow to allow users to view, restore, or permanently purge their soft-deleted documents:

1. New API Endpoints:
   • GET /api/v1/documents/trash: Lists all soft-deleted documents (is_deleted == True) belonging to the user or their active workspaces.
   • POST /api/v1/documents/{document_id}/restore: Restores a soft-deleted document by resetting is_deleted = False and deleted_at = None.
   • DELETE /api/v1/documents/{document_id}/purge: Immediately and permanently deletes the document's database record, physical uploads, vector chunks, and knowledge graph files.
2. Background Cleanup Integration:
   • Updated the daily cleanup_old_deleted_documents job to also purge knowledge graph files (delete_graph) of documents in trash for over 30 days.
3. Frontend UI Components:
   • Added a new TrashModal.tsx displaying trashed documents with options to restore or permanently purge them.
   • Integrated the Recycle Bin entry point inside DocumentSidebar.tsx as a trash button next to the "Documents" header.
4. Testing:
   • Created unit tests covering the new /trash, /restore, and /purge routes inside tests/test_documents.py.

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🗂️ Type of Change

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• 🐛 Bug fix
• ✨ New feature
• 🔧 Refactor / code cleanup
• 📝 Documentation update
• 🎨 UI / styling change
• ⚙️ CI / tooling / config change
• 🧪 Tests

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🧪 How was this tested?

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• Tested the affected API endpoints manually
• Added / updated tests (All 13 backend document tests passed successfully)
• Ran frontend local typecheck (npx tsc --noEmit completed with no compilation errors)

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⚠️ Anything to flag for reviewers?

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The new route GET /api/v1/documents/trash has been registered before GET /api/v1/documents/{document_id} in backend/app/routes/documents.py to prevent route matching conflicts where FastAPI would treat /trash as a document ID.

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✅ Self-Review Checklist

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• My branch is based on dev, not main
• I have not added any secrets / API keys
• I have not modified main branch or any HuggingFace deployment config
• My code follows the existing style (no unnecessary formatting changes)
• I have updated relevant docs / comments if needed

[param20h]

✅ This PR has been merged directly into dev by maintainer.