feat: add OpenAI-compatible provider shim — use any LLM with Claude Code

Adds a new 'openai' API provider that translates Anthropic SDK calls to
OpenAI chat completions format, enabling Claude Code's full tool system
(bash, file read/write/edit, grep, glob, agents) with any OpenAI-compatible
model: GPT-4o, DeepSeek, Gemini, Llama, Ollama, OpenRouter, and 200+ more.

Set CLAUDE_CODE_USE_OPENAI=1, OPENAI_API_KEY, and OPENAI_MODEL to use.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/utils/model/providers.ts

@@ -1,16 +1,18 @@
 import type { AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS } from '../../services/analytics/index.js'
 import { isEnvTruthy } from '../envUtils.js'
 
-export type APIProvider = 'firstParty' | 'bedrock' | 'vertex' | 'foundry'
+export type APIProvider = 'firstParty' | 'bedrock' | 'vertex' | 'foundry' | 'openai'
 
 export function getAPIProvider(): APIProvider {
-  return isEnvTruthy(process.env.CLAUDE_CODE_USE_BEDROCK)
-    ? 'bedrock'
-    : isEnvTruthy(process.env.CLAUDE_CODE_USE_VERTEX)
-      ? 'vertex'
-      : isEnvTruthy(process.env.CLAUDE_CODE_USE_FOUNDRY)
-        ? 'foundry'
-        : 'firstParty'
+  return isEnvTruthy(process.env.CLAUDE_CODE_USE_OPENAI)
+    ? 'openai'
+    : isEnvTruthy(process.env.CLAUDE_CODE_USE_BEDROCK)
+      ? 'bedrock'
+      : isEnvTruthy(process.env.CLAUDE_CODE_USE_VERTEX)
+        ? 'vertex'
+        : isEnvTruthy(process.env.CLAUDE_CODE_USE_FOUNDRY)
+          ? 'foundry'
+          : 'firstParty'
 }
 
 export function getAPIProviderForStatsig(): AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS {