feat: default watchlist semua, login-gate fitur, CI anti-stale via /api/version

backend/internal/store/migrations/0007_local_auth.sql

@@ -0,0 +1,6 @@
+-- FlowSight schema v7: local username+password login (Google stays optional).
+-- Local accounts store google_sub='local:<username>' so session scoping
+-- (sessions join + UserKeyForSub) works unchanged.
+ALTER TABLE users ADD COLUMN username TEXT;
+ALTER TABLE users ADD COLUMN password_hash TEXT NOT NULL DEFAULT '';
+CREATE UNIQUE INDEX IF NOT EXISTS idx_users_username ON users(username);