feat(provider): add vercel to all gateway-supported fallback entries

Adds vercel to every fallback entry where the model exists on the
gateway (kimi-k2.5, glm-5, glm-4.6v, minimax-m2.7, grok-code-fast-1,
gpt-5-nano). Adds inferSubProvider mappings for minimax, moonshotai,
and zai. Updates librarian/explore special cases to prefer minimax
via gateway over claude-haiku.

src/shared/provider-model-id-transform.ts

@@ -3,6 +3,9 @@ function inferSubProvider(model: string): string | undefined {
 	if (model.startsWith("gpt-")) return "openai"
 	if (model.startsWith("gemini-")) return "google"
 	if (model.startsWith("grok-")) return "xai"
+	if (model.startsWith("minimax-")) return "minimax"
+	if (model.startsWith("kimi-")) return "moonshotai"
+	if (model.startsWith("glm-")) return "zai"
 	return undefined
 }