fix: bake 文件写入项目根目录以修复 buildx context 缓存问题

bake JSON 原先写入系统临时目录，buildx 默认以 bake 文件所在目录作为
构建 context，导致 COPY . . 复制空目录，go build 命中旧的 mount cache
产出旧二进制，源码变更后镜像内容不变。改为写入项目根目录的 .bake.json。

.gitignore

@@ -126,3 +126,6 @@ DockerFile
 app/*/api/api
 app/*/rpc/rpc
 app/*/mq/mq
+
+# Build artifacts
+.bake.json

deploy/dev/build.py

@@ -5,7 +5,6 @@ import json
 import os
 import subprocess
 import sys
-import tempfile
 from glob import glob
 from pathlib import Path
 
@@ -100,21 +99,20 @@ def main():
         "target": targets,
     }
 
-    fd, bakefile = tempfile.mkstemp(prefix="juwan-bake-", suffix=".json")
+    bakefile = ROOT_DIR / ".bake.json"
     try:
-        with os.fdopen(fd, "w") as f:
-            json.dump(bake, f, indent=2)
+        bakefile.write_text(json.dumps(bake, indent=2))
         print(f"Generated {len(targets)} targets -> {bakefile}")
 
         names = list(targets.keys())
         for i in range(0, len(names), BAKE_BATCH_SIZE):
             batch = names[i : i + BAKE_BATCH_SIZE]
             subprocess.run(
-                ["docker", "buildx", "bake", "--load", "-f", bakefile, *batch],
+                ["docker", "buildx", "bake", "--load", "-f", str(bakefile), *batch],
                 check=True,
             )
     finally:
-        os.unlink(bakefile)
+        bakefile.unlink(missing_ok=True)
 
 
 main()