feat(templates): add meetings.template_id column (T8.1, FR-NOTE-5)

Templates themselves are a built-in Rust catalog, not a DB table —
this just remembers which one a meeting picked, so re-rendering
notes.md on reprocess/resume keeps the same section structure.

src-tauri/migrations/0006_note_templates.sql

@@ -0,0 +1,5 @@
+-- Note templates (Phase 8, T8.1, FR-NOTE-5). Templates themselves are a
+-- built-in Rust catalog (notes::templates), not a DB table — this column
+-- just remembers which one a meeting picked, so re-rendering notes.md on
+-- reprocess/resume keeps the same section structure instead of losing it.
+ALTER TABLE meetings ADD COLUMN template_id TEXT;