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/022_notes_query_index.sql

@@ -0,0 +1,21 @@
+-- Migration 022: Composite query indexes for notes + author_id column
+-- Optimizes author-scoped and project-scoped date-range queries on notes.
+-- Adds discussion JOIN indexes and immutable author identity column.
+
+-- Composite index for author-scoped queries (who command, notes --author)
+CREATE INDEX IF NOT EXISTS idx_notes_user_created
+ON notes(project_id, author_username COLLATE NOCASE, created_at DESC, id DESC)
+WHERE is_system = 0;
+
+-- Composite index for project-scoped date-range queries
+CREATE INDEX IF NOT EXISTS idx_notes_project_created
+ON notes(project_id, created_at DESC, id DESC)
+WHERE is_system = 0;
+
+-- Discussion JOIN indexes
+CREATE INDEX IF NOT EXISTS idx_discussions_issue_id ON discussions(issue_id);
+CREATE INDEX IF NOT EXISTS idx_discussions_mr_id ON discussions(merge_request_id);
+
+-- Immutable author identity column (GitLab numeric user ID)
+ALTER TABLE notes ADD COLUMN author_id INTEGER;
+CREATE INDEX IF NOT EXISTS idx_notes_author_id ON notes(author_id) WHERE author_id IS NOT NULL;