refactor(code): remove legacy single-repo worker modes

[danii1]

Summary

• remove legacy devintern worker --listen, devintern serve, --no-workspace, and cwd worker mode
• require every worker invocation to resolve an explicit or auto-detected workspace
• remove the duplicate repo-local polling, review, mention, relay, automation, dashboard, and webhook wiring from the CLI entrypoint
• simplify the shared worker daemon to workspace acquirers and keep direct webhooks exclusively under devintern webhook serve
• move recurring-automation documentation to workspace configuration and workspace-owned task files

Stack

• Depends on feat(code): add dedicated webhook serve command #68
• feat(code): add dedicated webhook serve command #68 introduces the canonical direct-webhook command; this PR removes the superseded paths

Validation

• focused CLI tests: 32 passed
• workspace-worker and worker-init tests: 25 passed
• full @getdevintern/code suite: 898 passed, 0 failed (with PR [DEV-86] Enable automatic conflict sync/resolution across all open PRs in the repo via configuration #67's exact fixture-isolation patch applied temporarily; that patch is not duplicated here)
• package lint, typecheck, and production build passed
• pre-commit monorepo format, lint, and typecheck passed