add endpoint and UI for users to update their own username

main.py

@@ -226,6 +226,23 @@ async def change_own_password(request: Request):
     conn.close()
     return {"status": "ok"}
 
+@app.put("/api/users/me/username", dependencies=[Depends(is_authenticated)])
+async def change_own_username(request: Request):
+    data = await request.json()
+    new_username = data.get("username")
+    if not new_username:
+        raise HTTPException(status_code=400, detail="New username required")
+    user_id = request.session.get("user_id")
+    try:
+        conn = sqlite3.connect(DB_PATH)
+        c = conn.cursor()
+        c.execute('UPDATE users SET username = ? WHERE id = ?', (new_username, user_id))
+        conn.commit()
+        conn.close()
+    except sqlite3.IntegrityError:
+        raise HTTPException(status_code=400, detail="Username already exists")
+    return {"status": "ok"}
+
 class InstanceCreate(BaseModel):
     name: str
     ip: str