fix(cookbook): lossless launch-command preview round-trip (#5979)

[Spoofiecus]

Summary

The Serve-panel command pipeline corrupted quoted $(...) model-arg commands across display->launch cycles: multi-line previews kept their \ continuations inline (uncollapsed), and the tokenizer fused backslash+space into \ --host tokens, compounding each edit. The launched shell passed a space-prefixed --model word, which llama-server rejects with error: invalid argument: --model (issue #5979).

Target branch

• This PR targets **dev**, not main. All PRs land in dev.

Type of Change

• Bug fix (non-breaking — fixes a confirmed issue)

Linked Issue

Fixes #5979

Checklist

• I searched open issues and open PRs — this is not a duplicate.
• This PR targets dev
• My changes are limited to the scope described above — no unrelated refactors or whitespace changes mixed in.
• I actually ran the app (uvicorn app:app, native venv) and verified the change works; details in How to Test.

How to Test

./venv/bin/python -m pytest tests/test_cookbook_serve_cmd_js.py — 6 passed (Node-driven: clean round trip, stable collapse, mangled-input self-heal, quoted escapes/spaces using the issue's exact $(printf %s ... ) model path, MODEL_FILE prelude, env-first ordering).
node --check static/js/cookbookServe.js static/js/cookbook.js — clean.
./venv/bin/python -m pytest tests/test_cookbook_serve_cmd_js.py tests/test_cookbook_helpers.py tests/test_cookbook_stale_shim_recovery.py — 97 passed, 1 skipped.
Rule 08: curl-served MD5 matches disk for cookbookServe.js + cookbook.js.
Live: dev :7001 serves the new bytes (healthy); original :7000 untouched.
Pre-existing 4-test baseline failures are the workspace baseline (rule 30), unrelated to this diff.

Scope is the editor/launch formatter only; no runner, API, backend arg-parsing, or mobile-sheet change. The PR that wraps this phase also carries the cache-buster bumps for the two touched JS files (rule 07).

Visual / UI changes

• Screenshot or short clip of the change in the running app, attached below.
• Style match: reuses existing cookbook panel styling; no new colors, fonts, spacing, or component patterns.
• No new component patterns. Extends the existing serve-panel command box.
• I am not an LLM agent submitting a bulk PR. Scoped single-issue fix for Invalid argument --model when trying to serve a model #5979 with tests and live verification.

Screenshots / clips

[Spoofiecus]