feat: Introduce note version history with dedicated UI, API, and database schema.

migrations/20251223030000_add_note_versions.sql

@@ -0,0 +1,11 @@
+-- Add note_versions table
+CREATE TABLE note_versions (
+    id TEXT PRIMARY KEY,
+    note_id TEXT NOT NULL,
+    title TEXT NOT NULL,
+    content TEXT NOT NULL,
+    created_at TEXT NOT NULL,
+    FOREIGN KEY(note_id) REFERENCES notes(id) ON DELETE CASCADE
+);
+
+CREATE INDEX idx_note_versions_note_id ON note_versions(note_id);