feat(storage): add summary/tags columns to the FTS5 search index

meeting_fts only ever indexed title/transcript/notes -- search silently
never covered summary or tags despite FR-SEARCH-1 requiring it (bug
report: "search not working" for those). meeting_fts is a derived index
(never a source of truth), so drop+recreate is safe: backfill_fts
repopulates every meeting from scratch on next startup.

src-tauri/migrations/0007_fts_summary_tags.sql

@@ -0,0 +1,17 @@
+-- Bug fix: search (FR-SEARCH-1) never covered summary or tags -- meeting_fts
+-- only ever had title/transcript_text/notes_text columns. `meeting_fts` is a
+-- derived index (rebuilt from meetings/transcript.json/notes.md/summary.json/
+-- tags, never a source of truth), so dropping and recreating it is safe: no
+-- data loss, and `backfill_fts` repopulates every meeting on next startup
+-- since a freshly created table has no rows for anything yet.
+DROP TABLE meeting_fts;
+
+CREATE VIRTUAL TABLE meeting_fts USING fts5(
+    meeting_id UNINDEXED,
+    title,
+    transcript_text,
+    notes_text,
+    summary_text,
+    tags_text,
+    tokenize = 'porter unicode61'
+);