fix(ci): chmod 700 /root/.ssh in GenerateBuildHistory container

Dagger mounts the secret file with 0600 but the parent directory may
get created with world-readable permissions, causing SSH to refuse
the key with exit 255.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ci/main.go

@@ -524,6 +524,7 @@ func (m *Ci) GenerateBuildHistory(
 		From("python:3.12-alpine").
 		WithExec([]string{"apk", "add", "--no-cache", "openssh-client"}).
 		WithMountedSecret("/root/.ssh/id_ed25519", sshKey, dagger.ContainerWithMountedSecretOpts{Mode: 0600}).
+		WithExec([]string{"chmod", "700", "/root/.ssh"}).
 		WithEnvVariable("SSH_USER", sshUser).
 		WithEnvVariable("SSH_HOST", sshHost).
 		WithDirectory("/src", scriptSource).