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.

bot_bottle/agent_provider.py

@@ -61,6 +61,13 @@ class AgentProviderRuntime:
     prompt_mode: PromptMode
     bypass_args: tuple[str, ...]
     resume_args: tuple[str, ...]
+    # argv run inside a throwaway container of a freshly built agent
+    # image, right after `build_image()`, to catch a build that
+    # exited 0 but produced a broken CLI (e.g. an npm
+    # optionalDependencies fetch for a platform-native binary that
+    # silently no-ops on a transient failure). Empty tuple skips the
+    # check — not every provider has opted in yet.
+    smoke_test: tuple[str, ...] = ()
 
 
 @dataclass(frozen=True)