docs(code-runtime-python): register the pythonBin load-rejection change; harden PYABS

The review's follow-ups: (1) the product-visible change (an unresolvable
basename pythonBin now fails at load instead of a run-time ENOENT worker-exit)
is registered in the settlement note, paired. (2) PYABS falls back to the bare
name when python3 is not resolvable, instead of interpolating the literal
'undefined' into the wrappers.

packages/code-runtime/code-runtime-python/tests/runtime.spec.ts

@@ -14,7 +14,7 @@ import type { Config } from '../src/index.ts'
 // interpreters only reachable through the caller's PATH (Nix, pyenv). Baking
 // the resolved absolute path mirrors what resolvePythonBin does for the product
 // spawn.
-const PYABS = resolvePythonBin('python3')
+const PYABS = resolvePythonBin('python3') ?? 'python3'
 import type { CodeBindingFunction, CodeJsonValue, CodeRunResult } from '@deepseek-ai/dsh-code-runtime'
 
 /**