fix(action image): 安裝 git 供前置遠端驗證使用

app/git.js

@@ -13,7 +13,10 @@ function makeRunner(spawn) {
     const opts = { cwd, encoding: 'utf8' };
     if (env) opts.env = env;
     const result = spawn('git', args, opts);
-    if (result.error) throw result.error;
+    if (result.error) {
+      if (result.error.code === 'ENOENT') throw new Error('找不到 git 指令，請確認 action image 已安裝 git');
+      throw result.error;
+    }
     if (result.status !== 0) throw new Error((result.stderr || result.stdout || '').trim());
     return (result.stdout || '').trim();
   };

app/git.test.js

@@ -300,6 +300,15 @@ describe('verifyRemoteAccess', () => {
     assert.match(result.error, /could not read Username/);
   });
 
+  it('reports a clear failure when git is not installed', () => {
+    const enoent = new Error('spawnSync git ENOENT');
+    enoent.code = 'ENOENT';
+    const spawn = () => ({ status: null, stdout: '', stderr: '', error: enoent });
+    const result = verifyRemoteAccess(workspace, spawn);
+    assert.equal(result.ok, false);
+    assert.match(result.error, /找不到 git 指令/);
+  });
+
   it('cleans up the askpass script after running', () => {
     verifyRemoteAccess(workspace, () => ({ status: 0, stdout: '', stderr: '', error: null }));
     const leftover = fs.readdirSync(workspace).filter(f => f.endsWith('.git-askpass.sh'));