docs(cli): complete task and chat budget help

[santoshkumarradha]

The main help synopsis omitted supported task model/worker flags and chat budget flags, and its shared headless-work explanation contained a garbled sentence. The summary now names those options and explains that chat budgets require --yolo.

Part of #1558. The token-count correction is already present in #1604. The engine command's deliberate omission from public help and home-relative workspace semantics are unchanged. Includes the existing test-only model-pin fixture correction from #1615 so full CLI verification preserves its disabled load gates.

Validation: final head 72c8ff1a4f5cfd7a547d96ea4e6e9374e5db444b passed Spark make pr-ready (exit 0; complete CLI package 191.015 seconds) and all GitHub checks. Built with make build; actual --help, do --help, and chat --help all exit 0 and include the missing options. Existing help layout tests pass with the original page/column limits unchanged. No model call is needed for this help-only change.

Evidence: extended/1558-ready.log/.exit, 1558-check-host.txt, 1558-check-revision.txt, 1558-layout-pass.log, 1558-final-cli-verification.json and the three 1558-final-help-*.txt captures. Initial help-layout failures are preserved; the correction shortened existing prose instead of raising layout limits.

[santoshkumarradha]

Superseded by the consolidated draft #1627. Exact reviewed head 72c8ff1a4f5cfd7a547d96ea4e6e9374e5db444b is included in published Santosh/dev integration ef1ba797ab6adbf4ff519d5808316d07d982c002; ancestry was verified after push. Source findings, validation, recordings and limitations are preserved in #1627. This closes the separate review destination; dev/main were not merged and final aggregate acceptance is still pending.