Story 6.4: Apply should-fix corrections from validation

Applied quality improvements identified during PO validation:

1. **Task 1 enhancements:**
   - Added multi-container service handling (e.g., Lowcoder with 3 containers)
   - Added /var/log directory creation with proper permissions
   - Ensures atomic updates for services with multiple containers

2. **Task 3 enhancements:**
   - Added Docker Hub API authentication support via DOCKER_HUB_TOKEN
   - Implemented rate limiting handling with exponential backoff
   - Added fallback to `docker compose pull --dry-run` if API fails
   - Documented token generation process

3. **Testing section improvements:**
   - Added explicit rollback test procedure (test #8)
   - Tests simulated update failure with non-existent version
   - Verifies rollback functionality restores previous version

4. **Accuracy corrections:**
   - Corrected service count from 14 to 12 (matches tech stack)
   - Updated references in Testing and Dev Notes sections

All 12 BorgStack services now properly documented in Task 6.
Story ready for dev agent implementation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: docg1701