fix(emby): bound Episodes-Latest ancestor fanout

[Pukabyte]

Summary

• fail open Episodes-Latest dashboard rewrites when the ancestor list has 30 or more entries
• retain the optimized rewrite for smaller ancestor lists
• add a 30-ancestor contract test that verifies source-SQL fallback and result parity

Validation

• linked emby_fts_rewrite_smoke suite passes

This is deliberately scoped to the large Episodes-Latest ancestor-list shape; other rewrite modes are unchanged.