[Bug]: Playground Advanced Config panel is non-functional — still sends the removed `code` protocol to /config/dump

Follow-up to #2222 / #2224. That PR stopped md/llm from being collateral damage. The underlying problem is still here, and it now fails more quietly than before.

What's wrong

The playground's Advanced Config panel still speaks the {type, code} protocol that /config/dump dropped in the 0.8.x security work. code is a globally forbidden field under the untrusted trust boundary, so the pre-flight always 400s:

CrawlerRunConfig.load({"type": "CrawlerRunConfig", "code": "..."}, provenance=Provenance.UNTRUSTED)
→ UntrustedConfigError: field 'code' is not permitted on CrawlerRunConfig from an untrusted request

crawl and crawl_stream survive only because of the regex fallback in runCrawl() (deploy/docker/static/playground/index.html), which checks the editor text for stream=True. Two consequences:

1. Config is silently discarded. With the default snippet CrawlerRunConfig(stream=True, cache_mode=CacheMode.BYPASS), the fallback sends {crawler_config: {type: 'CrawlerRunConfig', params: {stream: true}}}. The cache_mode line never reaches the server. The run succeeds, so nothing tells the user their config was dropped. Anything they type beyond stream is ignored.
2. BrowserConfig is a hard failure. That template has no stream=True, so no fallback fires and the run aborts with ✖ config error.

So the panel is non-functional on the only endpoint that still displays it.

Why it can't be patched in place

/config/dump used to eval the snippet. That was removed on purpose — it was a gadget-construction oracle. A Python-snippet editor can't work against the current server, so this isn't a matter of fixing the request shape.

Options

• Replace the CodeMirror Python editor with a params/JSON editor that posts {type, params}, which is what /config/dump accepts today. Keeps the feature, matches the server.
• Remove the panel. /crawl is still fully usable through the API; the playground just stops advertising a capability it doesn't have.

Either way the regex fallback in runCrawl() should go — it exists only to paper over the broken pre-flight, and it's what makes the config loss silent.

Repro

1. Start the Docker server, open /playground/
2. Endpoint crawl, default snippet, Run → succeeds, but cache_mode was never sent
3. Switch Type to BrowserConfig, Run → ✖ config error, run aborts

Notes

• Minor, same area: #cfg-status is written only by pyConfigToJson(). Since #2224, md/llm skip that call, so a stale ✖ config error from a previous crawl run stays on screen.