Make Data Machine optional for DMC core

[chubes4]

Summary

• Remove the hard Data Machine plugin requirement so DMC core can boot standalone.
• Add DMC-owned permission/settings facades that delegate to Data Machine when present and fall back to WordPress capabilities/options otherwise.
• Keep Data Machine bundle/handler/runtime integration behind optional registration while preserving the existing hooks when Data Machine is available.
• Add a standalone bootstrap smoke proving core workspace/GitHub/GitSync/code-task abilities register without Data Machine classes.

Why

This is the first boundary cleanup toward making the blessed workspace executor reusable outside Data Machine. Agents API remains the generic task/executor contract; DMC core can now carry the concrete workspace/git/GitHub executor surface without requiring Data Machine orchestration to be installed.

Verification

• homeboy lint --changed-only passed before commit on the changed files.
• php tests/smoke-standalone-bootstrap.php
• php tests/smoke-agents-api-workspace-executor-adapter.php

Note: full-tree homeboy lint still reports the existing PHPStan baseline drift outside this change (workspace metadata/reader/writer files). The changed-file lint was clean.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the bootstrap split, facades, standalone smoke coverage, verification, and PR description; Chris remains responsible for review and merge.