Add comprehensive code review instructions from 455 PRs

Extracted and analyzed 2,733 review comments across all 455 PRs with reviews
in this repository (Dec 2025 - Jul 2026). Used parallel analysis agents to
synthesize patterns by theme: security, performance, testing, maintainability,
and manifest/schema coherence.

Key sections:
- False-positive avoidance (patterns Copilot should NOT flag)
- Security (fail-closed checks, DLL hijacking, policy bypass, secret leaks)
- Rust patterns (caching, API visibility, error handling, FFI safety, what-if)
- Pester testing (cross-platform, isolation, assertions, structure)
- PowerShell adapters (module arrays, parallel scoping, error types)
- Design (settings precedence, backward compat, schema coherence)
- CI/CD (fork permissions, artifact contracts, control flow)
- Documentation (comments, logging, i18n accuracy)

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: SteveL-MSFT