Refactor/wangbinqi/code

[suguanYang]

Summary

• Refactor API and worker route handlers into service-level workflows for authentication, billing, job ingestion, callbacks, S3 events, retrieval, parsing, and worker job lifecycle logic.
• Keep behavior coverage in contract suites around API, worker, job lifecycle, parser, billing, webhook, S3 event, QStash, retrieval, and demo-document behavior.
• Resolve follow-up CodeQL findings from the refactor and remove implementation-seam tests from the contract test path.

Verification

• GitHub PR CI passed on the current head: Lint, Typecheck, Test, Gitleaks, CodeQL, and api/worker build jobs.
• Local targeted syntax check: python3 -m py_compile apps/api/app/services/demo_source_projection.py apps/worker/app/services/document_ingestion/processing_billing.py apps/worker/app/services/document_parser/doc_profile_pdf.py
• Local full test run was not performed in this environment because fetching the full PR checkout was unreliable; GitHub CI completed the authoritative branch validation.

Deployment Notes

• No new or changed environment variables.
• No database migrations.
• No release-order requirement identified.
• No known breaking API or worker contract change intended.

Checklist

• Tests were added or updated when behavior changed
• Public docs, examples, or OpenAPI contracts were updated when needed
• Database migrations are idempotent and safe to deploy
• Logs, errors, and validation paths avoid leaking secrets or user data
• The pull request description explains any breaking or user-visible change