chore: implement instruction compliance remediation

- Replace Go interface{} with any (Go 1.18+ standard)
- Add database indexes to frequently queried model fields
- Add JSDoc documentation to frontend API client methods
- Remove deprecated docker-compose version keys
- Add concurrency groups to all 25 GitHub Actions workflows
- Add YAML front matter and fix H1→H2 headings in docs

Coverage: Backend 85.5%, Frontend 87.73%
Security: No vulnerabilities detected

Refs: docs/plans/instruction_compliance_spec.md

docs/github-setup.md

@@ -1,4 +1,9 @@
-# 🔧 GitHub Setup Guide
+---
+title: GitHub Setup Guide
+description: Configure GitHub Actions for automatic Docker builds and documentation deployment for Charon.
+---
+
+## GitHub Setup Guide
 
 This guide will help you set up GitHub Actions for automatic Docker builds and documentation deployment.