🐛 Fix: prevent preview refresh during file upload

[cj2026-bit]

Summary

• remove duplicate documentsUpdated dispatch from upload polling
• keep preview close handling independent from parent callback identity
• skip redundant document context updates when polling data is unchanged
• remove noisy knowledge-base filter console logging

Impact review

• document status, progress, add, delete, reorder, and error changes still update the document list
• knowledge-base switching and creation flows retain their existing update paths
• preview access errors still close the drawer through the latest callback
• no backend, database, ES, AIDP, or Nexent SDK changes

Verification

• frontend Node tests: 72 passed across 24 files
• npm run type-check: passed
• npm run build: passed
• npm run lint: existing develop baseline has widespread Prettier/unused-variable failures; no new failure from the changed logic
• manual reproduction logs confirmed the original duplicate event and callback-identity chain before this fix

Test scenario

Upload a processing file, open an existing text preview, and keep it open during polling. Polling may continue, but the preview must not restart from Range 0 or repeatedly run its loading effect.