feat(code): add dedicated webhook serve command

[danii1]

Summary

• add devintern webhook serve as the canonical advanced repo-local direct-webhook service
• keep devintern serve as a deprecated alias and deprecate combined devintern worker --listen
• let legacy worker --listen run repo-locally even when a workspace is auto-detected, while rejecting an explicitly combined workspace
• update CLI help, generated service commands, configuration scaffolding, and deployment documentation

Stack

• Depends on feat(code): complete worker initialization wizard #66
• This is the first follow-up layer; cwd worker mode deprecation and final legacy cleanup are separate stacked PRs

Validation

• focused CLI tests: 31 passed
• worker mode and worker-init tests: 20 passed
• package typecheck, lint, and production build passed
• pre-commit monorepo format, lint, and typecheck passed
• full pre-push suite reached 900 passed with one unrelated AutomationAcquirer fixture failure caused by ambient /tmp config; the exact fixture isolation fix is already in [DEV-86] Enable automatic conflict sync/resolution across all open PRs in the repo via configuration #67