feat(ai): provider factories, per-provider catalogs, createProvider (phase 3)

Auth helpers in src/auth/helpers.ts: envApiKeyAuth() (stored key wins,
then env vars in order, with secret-prompt login) and lazyOAuth()
(flow loads on first use through bundler-opaque dynamic imports in
utils/oauth/load.ts; the OAuthAuth flow exports land in phase 4).
There is no OAuth factory toggle: providers that support OAuth always
attach it, advertising costs nothing until login/refresh runs.

createProvider() in models.ts builds providers from parts: single API
implementation or a map dispatched on model.api (mixed-API providers
like opencode and github-copilot); unknown api yields a stream error.

generate-models.ts now emits one providers/<id>.models.ts catalog per
provider (35 files, biome-excluded like models.generated.ts) and
models.generated.ts becomes a generated aggregator, so importing one
provider factory pulls one catalog. Typed getModel globals unchanged.

One factory per built-in provider under src/providers/: envApiKeyAuth
for standard providers, OAuth for anthropic/openai-codex/github-copilot,
ambient ApiKeyAuth for amazon-bedrock (AWS env/profile/IAM) and
google-vertex (explicit key or ADC+project+location).

providers/all.ts: builtinProviders(), builtinModels(), getBuiltin*
re-exports. fauxProvider() factory returns a real Provider for tests;
legacy registerFauxProvider() unchanged.

packages/ai/src/providers/all.ts

@@ -0,0 +1,92 @@
+import { type CreateModelsOptions, createModels, type MutableModels, type Provider } from "../models.ts";
+import { amazonBedrockProvider } from "./amazon-bedrock.ts";
+import { antLingProvider } from "./ant-ling.ts";
+import { anthropicProvider } from "./anthropic.ts";
+import { azureOpenAIResponsesProvider } from "./azure-openai-responses.ts";
+import { cerebrasProvider } from "./cerebras.ts";
+import { cloudflareAIGatewayProvider } from "./cloudflare-ai-gateway.ts";
+import { cloudflareWorkersAIProvider } from "./cloudflare-workers-ai.ts";
+import { deepseekProvider } from "./deepseek.ts";
+import { fireworksProvider } from "./fireworks.ts";
+import { githubCopilotProvider } from "./github-copilot.ts";
+import { googleProvider } from "./google.ts";
+import { googleVertexProvider } from "./google-vertex.ts";
+import { groqProvider } from "./groq.ts";
+import { huggingfaceProvider } from "./huggingface.ts";
+import { kimiCodingProvider } from "./kimi-coding.ts";
+import { minimaxProvider } from "./minimax.ts";
+import { minimaxCnProvider } from "./minimax-cn.ts";
+import { mistralProvider } from "./mistral.ts";
+import { moonshotaiProvider } from "./moonshotai.ts";
+import { moonshotaiCnProvider } from "./moonshotai-cn.ts";
+import { nvidiaProvider } from "./nvidia.ts";
+import { openaiProvider } from "./openai.ts";
+import { openaiCodexProvider } from "./openai-codex.ts";
+import { opencodeProvider } from "./opencode.ts";
+import { opencodeGoProvider } from "./opencode-go.ts";
+import { openrouterProvider } from "./openrouter.ts";
+import { togetherProvider } from "./together.ts";
+import { vercelAIGatewayProvider } from "./vercel-ai-gateway.ts";
+import { xaiProvider } from "./xai.ts";
+import { xiaomiProvider } from "./xiaomi.ts";
+import { xiaomiTokenPlanAmsProvider } from "./xiaomi-token-plan-ams.ts";
+import { xiaomiTokenPlanCnProvider } from "./xiaomi-token-plan-cn.ts";
+import { xiaomiTokenPlanSgpProvider } from "./xiaomi-token-plan-sgp.ts";
+import { zaiProvider } from "./zai.ts";
+import { zaiCodingCnProvider } from "./zai-coding-cn.ts";
+
+export {
+	getModel as getBuiltinModel,
+	getModels as getBuiltinModels,
+	getProviders as getBuiltinProviders,
+} from "../models.ts";
+
+/** All built-in providers, freshly constructed. */
+export function builtinProviders(): Provider[] {
+	return [
+		amazonBedrockProvider(),
+		antLingProvider(),
+		anthropicProvider(),
+		azureOpenAIResponsesProvider(),
+		cerebrasProvider(),
+		cloudflareAIGatewayProvider(),
+		cloudflareWorkersAIProvider(),
+		deepseekProvider(),
+		fireworksProvider(),
+		githubCopilotProvider(),
+		googleProvider(),
+		googleVertexProvider(),
+		groqProvider(),
+		huggingfaceProvider(),
+		kimiCodingProvider(),
+		minimaxProvider(),
+		minimaxCnProvider(),
+		mistralProvider(),
+		moonshotaiProvider(),
+		moonshotaiCnProvider(),
+		nvidiaProvider(),
+		openaiProvider(),
+		openaiCodexProvider(),
+		opencodeProvider(),
+		opencodeGoProvider(),
+		openrouterProvider(),
+		togetherProvider(),
+		vercelAIGatewayProvider(),
+		xaiProvider(),
+		xiaomiProvider(),
+		xiaomiTokenPlanAmsProvider(),
+		xiaomiTokenPlanCnProvider(),
+		xiaomiTokenPlanSgpProvider(),
+		zaiProvider(),
+		zaiCodingCnProvider(),
+	];
+}
+
+/** A `Models` collection with every built-in provider registered. */
+export function builtinModels(options?: CreateModelsOptions): MutableModels {
+	const models = createModels(options);
+	for (const provider of builtinProviders()) {
+		models.setProvider(provider);
+	}
+	return models;
+}