refactor: clarify job, check, and workflow delivery boundaries

[Kingson4Wu]

Summary

• Move task preparation, shell check execution, and the manual remote workflow template into focused modules.
• Share checked patch artifact validation across implementation workflows and require the patch base commit record.
• Update architecture and usage documentation and add behavioral tests for delivery gates.

Verification

• pnpm verify:local passed: 112 tests, 13 actionlint workflows, build, package, and audit.
• Commit signature verified locally.