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

.github/workflows/auto-label-issues.yml

@@ -4,6 +4,10 @@ on:
   issues:
     types: [opened, edited]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.issue.number }}
+  cancel-in-progress: true
+
 jobs:
   auto-label:
     runs-on: ubuntu-latest