Adds the unified file manager view (Windows Explorer-style), collapsible
folder tree sidebar item, full vitest test suite (55 tests, 4 files), and
commits all Phase 4 backend/frontend fixes that were staged but uncommitted.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Includes planning artifacts (03-CONTEXT, 03-DISCUSSION-LOG, 03-02-SUMMARY),
integration test script, MinIO/auth/docker fixes, and local dev account reference.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>