Add host bootstrap and repair helpers

Add a dedicated pyro host surface for supported chat hosts so Claude Code, Codex, and OpenCode users can connect or repair the canonical MCP setup without hand-writing raw commands or config edits.

Implement the shared host helper layer and wire it through the CLI with connect, print-config, doctor, and repair, all generated from the same canonical pyro mcp serve command shape and project-source flags. Update the docs, public contract, examples, changelog, and roadmap so the helper flow becomes the primary onramp while raw host-specific commands remain as reference material.

Harden the verification path that this milestone exposed: temp git repos in tests now disable commit signing, socket-based port tests skip cleanly when the sandbox forbids those primitives, and make test still uses multiple cores by default but caps xdist workers to a stable value so make check stays fast and deterministic here.

Validation:
- uv lock
- UV_OFFLINE=1 UV_CACHE_DIR=.uv-cache make check
- UV_OFFLINE=1 UV_CACHE_DIR=.uv-cache make dist-check

src/pyro_mcp/vm_environments.py

@@ -19,7 +19,7 @@ from typing import Any
 from pyro_mcp.runtime import DEFAULT_PLATFORM, RuntimePaths
 
 DEFAULT_ENVIRONMENT_VERSION = "1.0.0"
-DEFAULT_CATALOG_VERSION = "4.1.0"
+DEFAULT_CATALOG_VERSION = "4.2.0"
 OCI_MANIFEST_ACCEPT = ", ".join(
     (
         "application/vnd.oci.image.index.v1+json",
@@ -48,7 +48,7 @@ class VmEnvironment:
     oci_repository: str | None = None
     oci_reference: str | None = None
     source_digest: str | None = None
-    compatibility: str = ">=4.1.0,<5.0.0"
+    compatibility: str = ">=4.2.0,<5.0.0"
 
 
 @dataclass(frozen=True)