fix: run init_db with panel venv python

Use venv interpreter so werkzeug is available; sync admin user from .env on init.
Set default panel username to dekun.

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

panel/db.py

@@ -44,14 +44,13 @@ def init_db(env: dict[str, str]) -> None:
     username = env.get("PANEL_USERNAME", "admin")
     password = env.get("PANEL_PASSWORD")
     if not password:
-        raise SystemExit("请在 .env 中设置 PANEL_PASSWORD（运行 generate-keys.sh 可自动生成）")
+        raise SystemExit("请在 .env 中设置 PANEL_PASSWORD")
 
-    row = conn.execute("SELECT id FROM admin WHERE username = ?", (username,)).fetchone()
-    if row is None:
-        conn.execute(
-            "INSERT INTO admin (username, password_hash) VALUES (?, ?)",
-            (username, generate_password_hash(password)),
-        )
+    conn.execute("DELETE FROM admin")
+    conn.execute(
+        "INSERT INTO admin (username, password_hash) VALUES (?, ?)",
+        (username, generate_password_hash(password)),
+    )
 
     count = conn.execute("SELECT COUNT(*) AS c FROM nodes").fetchone()["c"]
     if count == 0: