feat: add host process capability contract

[chubes4]

Summary

• declare generic process and writable-workspace capabilities from the installed WordPress integration
• require the installed host to meet every CLI process prerequisite even when an earlier provider supplies a truthy process capability; later false denials continue to override the declaration
• invoke setsid through the portable setsid PROGRAM [ARGS...] contract shared by GNU and BusyBox, with deterministic argv coverage
• route the existing writable-content consumer through the writable-workspace declaration and verify installed hooks

Closes #557

Validation

• php -d zend.assertions=1 -d assert.exception=1 tests/wordpress-integration-package.php
• php tests/smoke-cli-transport.php
• bash tests/integration-adapters.sh
• ./tests/cli-transport-install.sh
• ./tests/wp-cli-transport-resolution.sh
• bash tests/installation-profile.sh
• ./tests/ci-coverage.sh
• PHP lint on touched PHP files; git diff --check

The package test covers capable, disabled, and missing states for every required PHP primitive plus a missing session launcher. The smoke test verifies that an incoming truthy declaration is rechecked against the installed complete contract, a later false denial wins, and the portable setsid argv keeps the child command first. This macOS runner lacks setsid, so execution-only assertions correctly skip after the capability checks.

AI assistance

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