Add curator roles/permissions with Users admin, and fix lineage branch joins.

Staff accounts use admin/curator roles and fine-grained flags; transitions connect source-to-target with color gradients and stream cutout masks so overlaps stay seamless.

Co-authored-by: Cursor <cursoragent@cursor.com>

db/migrate-user-roles.sql

@@ -0,0 +1,35 @@
+-- Staff roles and fine-grained permissions on users
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM information_schema.columns
+    WHERE table_schema = 'public' AND table_name = 'users' AND column_name = 'role'
+  ) THEN
+    ALTER TABLE users ADD COLUMN role VARCHAR(32) NOT NULL DEFAULT 'curator';
+    ALTER TABLE users ADD COLUMN permissions TEXT[] NOT NULL DEFAULT '{}';
+    ALTER TABLE users ADD COLUMN is_active BOOLEAN NOT NULL DEFAULT true;
+
+    -- Existing accounts were full curators; promote to admin so nothing breaks
+    UPDATE users
+    SET role = 'admin',
+        permissions = ARRAY[
+          'images',
+          'checkup',
+          'curator_notes',
+          'translations',
+          'influences',
+          'tours',
+          'users'
+        ]::text[];
+  END IF;
+END $$;
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint WHERE conname = 'users_role_check'
+  ) THEN
+    ALTER TABLE users ADD CONSTRAINT users_role_check CHECK (role IN ('admin', 'curator'));
+  END IF;
+END $$;