Problem:
The Explore page filter was sending visibility filter as:
  visibility in ["3", "2"]
when it should send:
  visibility in ["PUBLIC", "PROTECTED"]

The backend CEL filter parser expects string enum names, not numeric values.
This caused the Explore page to return no memos even when public memos existed.

Solution:
- Added getVisibilityName() helper to convert Visibility enum values to string names
- Updated useMemoFilters to use getVisibilityName() when building visibility filter
- Follows same pattern as existing getInstanceSettingKeyName() and getUserSettingKeyName()
- Added validation to warn on invalid enum values

Files changed:
- web/src/store/common.ts: Add getVisibilityName() helper with validation
- web/src/hooks/useMemoFilters.ts: Use getVisibilityName() in visibility filter

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>