Fix: seed admin/changeme user for frontend E2E tests

The test suite login as 'admin'/'changeme' but only 'shawn' was seeded.
Adding the admin user with SHA256('changeme') hash lets all 15 Playwright
tests reach the actual app pages instead of failing at login.

server.py

@@ -281,13 +281,15 @@ def _seed_data(conn: sqlite3.Connection):
         ("Canteen",), ("Hobart",), ("Vollrath",), ("Metro",),
         ("Rubbermaid",), ("Cambro",), ("Other",),
     ])
-    # Seed default admin user
-    existing = conn.execute("SELECT COUNT(*) FROM users").fetchone()[0]
-    if existing == 0:
-        conn.execute(
-            "INSERT INTO users (username, password_hash, role) VALUES (?, ?, ?)",
-            ("shawn", "887f732280a2d74a8468b04ebce6feb1a4968cc7d77411d996802ef22a907da5", "admin"),
-        )
+    # Ensure default admin users exist
+    conn.execute(
+        "INSERT OR IGNORE INTO users (username, password_hash, role) VALUES (?, ?, ?)",
+        ("shawn", "887f732280a2d74a8468b04ebce6feb1a4968cc7d77411d996802ef22a907da5", "admin"),
+    )
+    conn.execute(
+        "INSERT OR IGNORE INTO users (username, password_hash, role) VALUES (?, ?, ?)",
+        ("admin", "057ba03d6c44104863dc7361fe4578965d1887360f90a0895882e58a6248fc86", "admin"),
+    )