Crawl substrate is fixed to Anthropic web search — name it in the UI, then make it choosable

[mpstaton]

Context:

• Crawl-Substrate-Is-Fixed-To-Anthropic-Web-Search-Operator-Expected-A-Choice.md

Ascending ambition: (1) surface substrate + model in the crawl bar and provider field, (2) per-crawl model dial, (3) the plan's documented fallback substrate — connector packs + Haiku filter — behind a real choice, returning the palette to the agentic path.