[codex] chore(quality): add AI-assisted quality gates

[Shilo]

Summary

Adds a dev-only quality workflow for AI-assisted changes in Mimic:

• static Mimic policy checks for common AI/vibe-coding issues and public API docs
• locked jscpd duplicate-code detection with a committed clone baseline
• hash-locked gdcruiser dependency architecture checks
• checksum-verified gdstyle diagnostics with error-level safety gates
• GitHub Actions jobs for static quality and Godot regression coverage
• README and quick-start cleanup so user-facing docs stay focused on addon usage

Validation

• powershell -NoProfile -ExecutionPolicy Bypass -File tools/quality.ps1 -BootstrapTools
• powershell -NoProfile -ExecutionPolicy Bypass -File tools/verify.ps1
• powershell -NoProfile -ExecutionPolicy Bypass -File tools/verify.ps1 -SkipQuality
• python -m mkdocs build --strict
• git diff --check

Notes

The PR is draft until the new Linux Godot Regression GitHub Actions job runs green once. Local Windows verification is green, but the CI job is new.