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/codeql.yml

@@ -8,6 +8,13 @@ on:
   schedule:
     - cron: '0 3 * * 1'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  GO_VERSION: '1.25.5'
+
 permissions:
   contents: read
   security-events: write
@@ -42,7 +49,7 @@ jobs:
         if: matrix.language == 'go'
         uses: actions/setup-go@4dc6199c7b1a012772edbd06daecab0f50c9053c # v6
         with:
-          go-version: '1.25.5'
+          go-version: ${{ env.GO_VERSION }}
 
       - name: Autobuild
         uses: github/codeql-action/autobuild@5d4e8d1aca955e8d8589aabd499c5cae939e33c7 # v4