refactor (v2): better arch

Co-authored-by: Copilot <copilot@github.com>

crates/adapters/sqlite/migrations/20251231000001_nullable_note_version_title.sql

@@ -0,0 +1,16 @@
+-- note_versions.title should be nullable to match notes where title is optional
+CREATE TABLE note_versions_new (
+    id TEXT PRIMARY KEY,
+    note_id TEXT NOT NULL,
+    title TEXT,
+    content TEXT NOT NULL,
+    created_at TEXT NOT NULL,
+    FOREIGN KEY(note_id) REFERENCES notes(id) ON DELETE CASCADE
+);
+
+INSERT INTO note_versions_new SELECT id, note_id, NULLIF(title, ''), content, created_at FROM note_versions;
+
+DROP TABLE note_versions;
+ALTER TABLE note_versions_new RENAME TO note_versions;
+
+CREATE INDEX idx_note_versions_note_id ON note_versions(note_id);