fix: smoke-test agent images after build, add start --no-cache

npm treats optionalDependencies failures as non-fatal, so a transient
network blip fetching claude-code's platform-native binary during
`npm install -g` left a stub CLI in an image that still "built"
successfully — then got baked into the Docker/Container layer cache
until forced to rebuild. Post-build smoke test (provider-declared
argv, run in a throwaway container of the freshly built image) fails
the launch loudly instead of shipping a broken image; --no-cache
gives an escape hatch to force a from-scratch rebuild.

Closes #353.

tests/unit/test_smolmachines_launch_image.py

@@ -153,6 +153,7 @@ class TestAgentFromPath(unittest.TestCase):
             slug="dev-abc12",
             agent_image="bot-bottle-claude:latest",
             agent_dockerfile_path="/repo/Dockerfile",
+            agent_provider_template="claude",
         ))
 
     def test_uses_committed_artifact_when_present(self):
@@ -185,6 +186,7 @@ class TestAgentFromPath(unittest.TestCase):
         ensure.assert_called_once_with(
             "bot-bottle-claude:latest",
             dockerfile="/repo/Dockerfile",
+            smoke_test=("claude", "--version"),
         )