fix(research): Claude Opus 4.7 rejects temperature param + log executor errors

- claude-web-search.ts: only send `temperature` when caller explicitly
  sets one. Opus 4.7 deprecated the param and returns
  400 invalid_request_error "`temperature` is deprecated for this
  model." Sonnet/Haiku still accept it, so keep the opt-in path.
- execute-research.ts: log provider errors via console.warn so future
  integration failures are visible in stdout. Previously the executor
  swallowed the underlying error and only returned a generic errorCode,
  which made diagnosing vendor-specific API changes impossible.

Discovered via smoke-testing with a real Anthropic key — the direct
curl worked, but our provider 400'd because Opus 4.7 tightened the
accepted param set.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

services/mana-research/src/executor/execute-research.ts

@@ -133,6 +133,7 @@ export async function executeResearch(
 
 function makeError(providerId: ProviderId, t0: number, err: Error): ExecuteResearchOutput {
 	const code = (err as { code?: string }).code ?? err.name ?? 'ERROR';
+	console.warn(`[executor.research] ${providerId} failed:`, err.message, err);
 	return {
 		success: false,
 		meta: {