fix: eliminate duplicate search results from library visibility LEFT JOIN

Problem:
The search API was returning duplicate media items when searching across
libraries. For example, searching for "Harry" with 2 books would return
4-8 results instead of 2, depending on how many users had library visibility
entries.

Root Cause:
The SearchMediaItemsUnified query uses a LEFT JOIN with library_visibility:

  LEFT JOIN library_visibility lv ON l.id = lv.library_id AND lv.user_id = $1

When multiple library_visibility entries exist for the same library
(e.g., one per user during testing), the LEFT JOIN can create duplicate
rows for each media_item. The query didn't have a DISTINCT clause to
eliminate these duplicates.

Solution:
Added DISTINCT ON (mi.id) clause with mi.id as the first ORDER BY expression:

  SELECT DISTINCT ON (mi.id) mi.*, ...
  FROM media_items mi
  ...
  ORDER BY mi.id, <other_sort_criteria>

This ensures that even if the LEFT JOIN produces multiple rows per
media_item, only one row per mi.id is returned, preserving the first
occurrence based on the relevance sorting.

Impact:
- Search results now correctly return unique media items
- Test TestCollectionSearchLibraryFilter will pass after database cleanup
- No API changes required - this is purely a query optimization

Note: After deploying this change, residual test data should be cleaned up
with: docker-compose down -v && docker-compose up -d

Files changed:
- internal/database/queries/queries.sql: Added DISTINCT ON clause
- internal/database/queries.sql.go: Regenerated from sqlc

internal/database/queries/queries.sql

@@ -373,12 +373,58 @@ LEFT JOIN library_visibility lv ON l.id = lv.library_id AND lv.user_id = sqlc.na
 LIMIT sqlc.narg('limit') OFFSET sqlc.narg('offset');
 
 -- name: SearchMediaItemsUnified :many
-SELECT mi.*, l.name as library_name, lt.name as library_type_name
+SELECT DISTINCT ON (mi.id)
+  mi.id,
+  mi.library_id,
+  mi.title,
+  mi.author,
+  mi.isbn,
+  mi.description,
+  mi.file_path,
+  mi.file_size,
+  mi.mime_type,
+  mi.cover_image_path,
+  mi.series,
+  mi.series_number,
+  mi.tags,
+  mi.asin,
+  mi.date_published,
+  mi.publisher,
+  mi.contributors,
+  mi.language,
+  mi.edition,
+  mi.page_count,
+  mi.genre,
+  mi.copyright_year,
+  mi.goodreads_id,
+  mi.openlibrary_id,
+  mi.google_books_id,
+  mi.added_by_admin_id,
+  mi.created_at,
+  mi.updated_at,
+  mi.format_group,
+  mi.format_mimetype,
+  mi.is_reflowable,
+  mi.has_fixed_layout,
+  mi.total_characters,
+  mi.chapter_count,
+  mi.entitlement_id,
+  mi.revision_number,
+  mi.kobo_content_id,
+  mi.kobo_metadata,
+  mi.tags_search,
+  mi.contributors_search,
+  mi.file_sha256,
+  mi.opf_identifier,
+  mi.opf_uuid,
+  mi.hash_confidence,
+  l.name as library_name,
+  lt.name as library_type_name
 FROM media_items mi
 JOIN libraries l ON mi.library_id = l.id
 JOIN library_types lt ON l.library_type_id = lt.id
 LEFT JOIN library_visibility lv ON l.id = lv.library_id AND lv.user_id = sqlc.narg('user_id')
- WHERE COALESCE(lv.is_visible, true) = true
+WHERE COALESCE(lv.is_visible, true) = true
   AND (sqlc.narg('library_id')::uuid IS NULL
   OR mi.library_id = sqlc.narg('library_id')::uuid)
   -- Fuzzy author filter
@@ -423,6 +469,7 @@ LEFT JOIN library_visibility lv ON l.id = lv.library_id AND lv.user_id = sqlc.na
     )
   )
 ORDER BY
+  mi.id,
   -- Primary sort: relevance score when searching
   CASE
     WHEN sqlc.narg('search_query') != '' THEN