Chat tests previously constructed a real `openai` provider with a fake
API key and no `BaseURL`, so background title generation hit
`api.openai.com` and timed out under `-race`. The same root cause
produced several distinct flakes: title regeneration races with
synchronous `UpdateChat`/`ProposeChatTitle`, and pagination races
against `updated_at` bumps from real-network processing.
This moves the fake OpenAI-compatible provider and the chat-settle wait
into first-class `coderdtest` capabilities.
`coderd.Options.ChatProviderAPIKeys` is the new seam tests use to
redirect chat traffic to a local `httptest.Server`.
`coderdtest.WaitForChatSettled` replaces per-test waiters and drains
tracked chat-daemon work after the chat row leaves `pending`/`running`.
The `newChatClient*` constructors funnel through one options builder
that installs the fake provider before the coderd test server so cleanup
ordering is deterministic.
Closes https://github.com/coder/internal/issues/1528 & Closes ENG-2659
Closes https://github.com/coder/internal/issues/1480 & Closes CODAGT-359
Closes https://github.com/coder/internal/issues/1507 & Closes CODAGT-368
Relates to https://github.com/coder/internal/issues/1397 & Relates to
CODAGT-374
Michael Suchacz