feat(huf-tables): add bulk import feature and permission bridge for HUF tables

[esafwan]

Summary

Adds a user-friendly Bulk Import feature for HUF Tables by building a lightweight wrapper around Frappe's native Data Import engine.

Key Changes

• Backend Permission Bridge (api.py):
  • Automatically sets allow_import=1 on generated HF {table_name} DocTypes at creation/update time.
  • Grants import DocPerms to System Manager and capability holders under flows.manage.
  • Added _ensure_import_enabled(): retrofits legacy HUF tables automatically.
  • Added 3 whitelisted API endpoints: get_bulk_import_template_url, start_table_bulk_import, and get_table_bulk_import_status.
• Frontend Bulk Import Modal (BulkImportModal.tsx):
  • Step 1: Download CSV template button.
  • Step 2: Drag-and-drop CSV upload via frappeFile.uploadFile.
  • Step 3: Start Import button with 2s live status polling showing success/failure counts and row-level error diagnostic breakdown.
  • Added Import Data button in DataTableViewPage.tsx header bar next to Add Record.

Proof of Test

Verification

• Built frontend with zero TypeScript errors (tsc -b && vite build).
• Verified Python compilation (python3 -m py_compile huf/huf/doctype/huf_data_table/api.py).
• Verified live bench container rendering at http://huf.localhost:8100/huf/data/:tableId.

[esafwan]

Superseded by consolidated Data Tables PR #460, now included in integration PR #468.