Add storage

cyynote-backend/target/classes/db/migrations/V3__note_userid_index.sql

@@ -0,0 +1,6 @@
+-- Ensure note.userid column exists (for older databases created before this field was added)
+ALTER TABLE note ADD COLUMN userid INTEGER DEFAULT 0;
+
+-- Index for faster per-user queries
+CREATE INDEX IF NOT EXISTS idx_note_userid ON note(userid);
+CREATE INDEX IF NOT EXISTS idx_note_flag_userid ON note(flag, userid);