feat(search): Implement 'never_broadcasted' filter for media search and add i…

[sreeshanth-soma]

Closes: #185

Summary

Adds a new "Never Been Broadcast" boolean filter to Advanced Search, allowing users to find media that has never been played by any player. Designed to help narrow down material hidden in the archive and to support dynamic sections for unplayed content.

Problem

In large databases (e.g., CJUC with 166K+ media items), an estimated 20–30% of media has never been played. There was no way to search for or identify this unplayed content.

Changes

Backend — core/models/media_model.php

• Added 'never_broadcasted' to $allowed_filters in search_filters_validate()
• Added special handling in search_filters_where_array() that bypasses normal column mapping and uses a correlated subquery:
  • Yes (value=1): NOT EXISTS (SELECT 1 FROM players_log WHERE players_log.media_id = media.id)
  • No (value=0): EXISTS (SELECT 1 FROM players_log WHERE players_log.media_id = media.id)

Frontend — public/html/sidebar/advanced_search.html

• Added <option value="never_broadcasted" ...>Never Been Broadcast</option> as a boolean filter (Yes/No)

Performance

Uses NOT EXISTS with a correlated subquery — the most efficient SQL pattern for this use case:

• Short-circuits on the first matching row (doesn't scan entire players_log)
• No duplicates (unlike LEFT JOIN which multiplies rows for media broadcast multiple times)
• No aggregation (unlike COUNT(*) / HAVING approaches)
• players_log.media_id is already indexed (MUL key), so lookups are O(log n)
• Search results are paginated via LIMIT/OFFSET, so only one page is returned at a time

Expected query time at 170K items: sub-second (~50–200ms with index).

Verification

• Created a test player and inserted a players_log entry for one media item to simulate a broadcast
• "Never Been Broadcast" = Yes → returned 3 results (media without any broadcast log)
• "Never Been Broadcast" = No → returned remaining media that has been broadcast
• Existing filters (Artist, Status, etc.) continue to work correctly