Fix ambiguous column in SQLite FTS multi-term search (#2688)

* Fix multi-term SQLite FTS5 search causing a 500 error

When filtering cards by more than one term, `matching` was called
once per term via an association join. Rails did not deduplicate
association joins, resulting in two JOINs to `search_records_fts`
in a single query. SQLite FTS5 then raised "ambiguous column name"
when evaluating the MATCH condition.

Fix by using a string join instead, which Rails deduplicates so
only one JOIN to `search_records_fts` is generated regardless of
how many terms are searched.

Fixes: https://github.com/basecamp/fizzy/discussions/2354

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* test: verify multi-term search requires ALL terms to match

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Mike Dalessio <mike@37signals.com>

app/models/search/record/sqlite.rb

@@ -10,7 +10,10 @@ module Search::Record::SQLite
 
     after_save :upsert_to_fts5_table
 
-    scope :matching, ->(query, account_id) { joins(:search_records_fts).where("search_records_fts MATCH ?", query) }
+    scope :matching, ->(query, account_id) {
+      joins("INNER JOIN search_records_fts ON search_records_fts.rowid = #{table_name}.id")
+        .where("search_records_fts MATCH ?", query)
+    }
   end
 
   class_methods do