docs: update story 05 to match actual CI implementation

- Updated CI workflow diagram to reflect 5-job structure
- Documented actual job flow: lint/test (parallel) → build/scan (parallel) → integration → summary
- Corrected golangci-lint version to v2.7.2 with v2 schema
- Updated security scanning: govulncheck moved to scan-docker-image job
- Added Trivy conditional SARIF upload logic
- Simplified coverage check to warning-only (not blocking)
- Removed outdated docker-build.yml and build-base.yml references
- Updated performance metrics to match current implementation
- Reduced content by 193 lines, keeping documentation concise

Author: chendelin1982