feat: implement per-note search and document pipeline

- Add SourceType::Note with extract_note_document() and ParentMetadataCache
- Migration 022: composite indexes for notes queries + author_id column
- Migration 024: table rebuild adding 'note' to CHECK constraints, defense triggers
- Migration 025: backfill existing non-system notes into dirty queue
- Add lore notes CLI command with 17 filter options (author, path, resolution, etc.)
- Support table/json/jsonl/csv output formats with field selection
- Wire note dirty tracking through discussion and MR discussion ingestion
- Fix test_migration_024_preserves_existing_data off-by-one (tested wrong migration)
- Fix upsert_document_inner returning false for label/path-only changes

migrations/025_note_dirty_backfill.sql

@@ -0,0 +1,8 @@
+-- Backfill existing non-system notes into dirty queue for document generation.
+-- Only seeds notes that don't already have documents and aren't already queued.
+INSERT INTO dirty_sources (source_type, source_id, queued_at)
+SELECT 'note', n.id, CAST(strftime('%s', 'now') AS INTEGER) * 1000
+FROM notes n
+LEFT JOIN documents d ON d.source_type = 'note' AND d.source_id = n.id
+WHERE n.is_system = 0 AND d.id IS NULL
+ON CONFLICT(source_type, source_id) DO NOTHING;