chore: consolidate 17 workflows into 6 optimized ones

Reduce GitHub Actions minute usage by consolidating workflows:

- ci.yml: Merged CI + quality.yml into single job with path filters,
  concurrency groups, and aggressive caching
- release.yml: Merged auto-release + docker + helm-repo + release +
  sbom + notify into sequential pipeline (version/docker/helm/notes)
- security.yml: Merged codeql + security + govulncheck into weekly
  single job with filesystem-only Trivy scan (no image builds)
- docs.yml: Optimized with docs/** path filter
- cleanup.yml: Merged cleanup + stale into single weekly job
- label.yml: Kept as-is with proper triggers re-enabled

Deleted: auto-release.yml, quality.yml, codeql.yml, docker.yml,
e2e.yml, govulncheck.yml, helm-repo.yml, notify.yml,
release-drafter.yml, sbom.yml, stale.yml

Key optimizations:
- Concurrency groups cancel superseded CI runs
- Path filters skip irrelevant steps (dorny/paths-filter)
- Single jobs where possible (no queue overhead)
- No multi-platform Docker builds (linux/amd64 only)
- Weekly security scans instead of per-push
- Estimated ~253 min/month vs 2,000 limit (12.6%)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: atulmgupta