Add Composer extension diagnostics

[josiahking]

Summary

Adds current-project Composer extension diagnostics to the default evolve doctor command.

Changes

• inspect runtime ext-* requirements from the current project's composer.json
• diagnose missing, unreadable, malformed, or structurally invalid Composer project manifests
• normalize and deterministically check declared PHP extensions
• keep require-dev excluded from runtime diagnostics
• wire project extension checks after the existing PHP version check
• add unit, binary integration, architecture, and documentation coverage

Validation

• full quality suite: 600 tests, 2,186 assertions
• PHPStan: clean
• PHP CS Fixer: clean
• Composer validation: clean
• security and supply-chain checks: clean
• prerelease consumer validation: clean
• deterministic package split validation: clean
• release validation: clean
• Core split SHA: d9b5c8f75fb6e7bed8f1be130dfc25d742f6a2f5

Current limits

This checks extension presence only. It does not perform Composer dependency solving, semver compatibility analysis, extension version-constraint evaluation, lock-file inspection, JSON output, route/environment/writable-path inspection, generators, or Bridge/Audit integration.