Gallery search built a single `%{search}%` LIKE, so multi-word queries only matched the exact adjacent phrase ("red car" missed "a car that is red") and literal % / _ acted as SQL wildcards. Split on whitespace and require each token to match (prompt OR tags OR ai_tags), escaping LIKE wildcards per token; same escaping for the tag filter. Promote _escape_like to public escape_like_pattern() shared helper.
Part of #2123.
Tests: tests/test_gallery_search_multiword.py (5 tests); 4 fail pre-fix, 5 pass post-fix. Neighbors (session_search, gallery null-user, shims): 25 passed.
_search_fts ran the FTS MATCH query, then looked up each hit's full row with its
own db.query(...).filter(id == message_id).first() inside a loop, so a search
returning N hits issued N extra SELECTs. Fetch all hit rows in a single IN(...)
query via _fetch_messages_by_id and reassemble results in hit (relevance) order.
Adds tests/test_session_search_batch_fetch.py asserting a single batched query
(and no query for empty input). Existing session-search tests stay green.
Merajul Arefin