refactor(agents): enforce senior engineering principles across all agents

[phuthuycoding]

Summary

• Add assets/architecture/_shared/engineering-principles.md — single source of truth for the senior bar every agent codes to:
  1. Simple first — never overengineer (YAGNI, complexity must be earned)
  2. Think business first (restate requirement, walk edge/failure paths, trace blast radius)
  3. Challenge the solution — fit / risk / worth it (does it suit THIS project, name risks, weigh cost vs benefit, push back before implementing)
  4. Senior-level code (explicit error handling + logging, no swallowed exceptions, ~500-line file ceiling)
  5. No garbage code (no dead code, debug leftovers, drive-by edits; reuse before writing)
  6. Comments must earn their place (only why/constraint, never narrate code)
• Add an Engineering Principles (NON-NEGOTIABLE) block to all 16 agents, tailored per role:
  • code-reviewer treats overengineering and garbage code as defects; reviews against the pattern the codebase actually uses
  • clean-architect must right-size recommendations (no 4-layer Clean Architecture for simple CRUD)
  • refactor applies design patterns only to remove real existing complexity, never speculatively
  • perf-optimizer, security-audit, test-writer, etc. get role-specific challenge/worth-it bullets
• Developer agents: replace "follow the architecture docs exactly" with match-the-project-first (read-project-first.md), consistent with the earlier skills refactor (92e6d0b)
• nodejs-backend-dev: DDD layer rules apply only when the project actually uses (or is migrating to) DDD
• Sync the Architecture References table in CLAUDE.md

Notes

• Installer symlinks/copies the whole architecture/ folder, so the new _shared file is picked up with no installer change; --project (copy) installs need a re-run of moicle install --project.