Add Insight diagnostic capture policy

[josiahking]

Summary

• add immutable primitive-only diagnostic capture entries and attributes
• add explicit diagnostic data classification with safe operational defaults
• add deterministic secret/authentication redaction and sensitive-name protection
• add exact category/name filtering and deterministic execution-level sampling
• enforce bounded attributes and first-accepted-wins duplicate handling
• document the capture-policy foundation and keep storage/runtime integration deferred

Validation

• Capture tests: 29 tests / 90 assertions
• Insight suite: 111 tests / 278 assertions with SQLite enabled
• package architecture checks passed
• PHPStan passed
• Deptrac passed
• PHP-CS-Fixer dry-run passed
• root PHPUnit passed with one environment-specific symlink skip
• strict Composer, release-package, security and licence checks passed
• deterministic package splits passed for all 13 packages
• prerelease consumer validation passed
• application skeleton/create-project validation passed