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/deepseek.models.ts

@@ -0,0 +1,45 @@
+// This file is auto-generated by scripts/generate-models.ts
+// Do not edit manually - run 'npm run generate-models' to update
+
+import type { Model } from "../types.ts";
+
+export const DEEPSEEK_MODELS = {
+	"deepseek-v4-flash": {
+		id: "deepseek-v4-flash",
+		name: "DeepSeek V4 Flash",
+		api: "openai-completions",
+		provider: "deepseek",
+		baseUrl: "https://api.deepseek.com",
+		compat: {"requiresReasoningContentOnAssistantMessages":true,"thinkingFormat":"deepseek"},
+		reasoning: true,
+		thinkingLevelMap: {"minimal":null,"low":null,"medium":null,"high":"high","xhigh":"max"},
+		input: ["text"],
+		cost: {
+			input: 0.14,
+			output: 0.28,
+			cacheRead: 0.0028,
+			cacheWrite: 0,
+		},
+		contextWindow: 1000000,
+		maxTokens: 384000,
+	} satisfies Model<"openai-completions">,
+	"deepseek-v4-pro": {
+		id: "deepseek-v4-pro",
+		name: "DeepSeek V4 Pro",
+		api: "openai-completions",
+		provider: "deepseek",
+		baseUrl: "https://api.deepseek.com",
+		compat: {"requiresReasoningContentOnAssistantMessages":true,"thinkingFormat":"deepseek"},
+		reasoning: true,
+		thinkingLevelMap: {"minimal":null,"low":null,"medium":null,"high":"high","xhigh":"max"},
+		input: ["text"],
+		cost: {
+			input: 0.435,
+			output: 0.87,
+			cacheRead: 0.003625,
+			cacheWrite: 0,
+		},
+		contextWindow: 1000000,
+		maxTokens: 384000,
+	} satisfies Model<"openai-completions">,
+} as const;