Detect missing Composer development tools in check-env

What

Harden bin/check-env.sh so it verifies the Composer development binaries required by documented quality commands, not only vendor/autoload.php.

Why

During #1805 the environment check reported Composer dependencies ready while vendor/bin/phpunit and vendor/bin/phpcs were absent after a production --no-dev install. The false positive delayed release verification.

Tier

tier:standard — the implementation is small, but the repository needs a verified shell-test pattern and clear recovery guidance for partially installed dependencies.

Files

• bin/check-env.sh
• Existing shell tests for environment checks, or a new focused test under the verified test-tooling location
• AGENTS.md only if documented output changes

Reference pattern

Follow the existing [OK] and failure-guidance output in bin/check-env.sh. Check executable presence for vendor/bin/phpunit, vendor/bin/phpcs, and vendor/bin/phpstan; recommend composer install when any required development binary is missing.

Implementation steps

1. Inspect existing prerequisite checks and shell-test conventions.
2. Add explicit executable checks for all Composer-backed quality commands.
3. Distinguish a production --no-dev install from a development-ready install.
4. Add a regression test for vendor/autoload.php present with vendor/bin tools absent.

Acceptance criteria

• The check fails when autoload exists but required development binaries do not.
• Recovery output identifies composer install.
• A complete development install still passes.
• ShellCheck and focused tests pass.

Verification

• bash bin/check-env.sh
• Focused shell test covering missing and present binaries
• shellcheck bin/check-env.sh

Dependency

Blocked by #1805; begin after PR #1806 merges.

aidevops.sh v3.32.317 plugin for OpenCode v1.18.29 with gpt-5.6-sol spent 4h 26m and 539,830 tokens on this with the user in an interactive session.

Start with bin/check-env.sh and the existing shell-test conventions. Reproduce the missing-development-tools case with vendor/autoload.php present while vendor/bin/phpunit, phpcs, and phpstan are absent, then compare it with a complete install. Verify the focused shell test, bash bin/check-env.sh, and shellcheck bin/check-env.sh; done means the missing case fails with composer install guidance and a complete install passes.