Reindex returns success with zero vectors when directory only contains .overview.md

[SonicBotMan]

Bug: Reindex returns "Indexed" with 0 vectors when target has empty .overview.md

Description

When calling POST /api/v1/maintenance/reindex on a URI where the only file is an empty .overview.md (auto-generated summary file), the API returns a successful "Indexed" response but produces zero vectors.

This gives a false positive — the user believes the reindex succeeded, but no meaningful content was actually indexed.

Steps to Reproduce

1. Have a resource directory that only contains an auto-generated .overview.md file (e.g., a directory that was created but has no actual content files yet)
2. Call reindex on that directory:

   curl -X POST http://localhost:1933/api/v1/maintenance/reindex \
     -H "Authorization: Bearer <token>" \
     -H "X-OpenViking-Account: wiki" \
     -H "X-OpenViking-User: wiki-user" \
     -H "Content-Type: application/json" \
     -d '{"uri": "viking://wiki/user/wiki-user/resources/empty-dir/"}'

3. Response: Success with "Indexed" status
4. Check vectors: 0 new vectors created

Expected Behavior

Either:

• Skip .overview.md files during reindex (they are metadata, not content), or
• Return a more informative response indicating how many files were actually indexed vs skipped

Additional Context

The index_resource() function in embedding_utils.py already skips hidden files starting with . (line ~368: if file_name.startswith("."): continue), so .overview.md IS being skipped. The issue is that when .overview.md is the only file in a directory, the reindex appears to succeed but indexed nothing. The response should reflect this.

Environment

• OpenViking v0.3.10
• Docker deployment