feat(cli): add openai provider support for OpenAI-compatible endpoints

Add the `openai` provider to the CLI's supported providers list,
enabling use of OpenAI-compatible API endpoints (e.g., locally deployed
LLMs via vLLM, llama.cpp, Ollama, LM Studio, etc.).

Changes:
- Add "openai" to supportedProviders in types.ts
- Add "openai" env var mapping (OPENAI_API_KEY) in provider.ts
- Add "openai" case in getProviderSettings() with support for
  OPENAI_BASE_URL environment variable for custom endpoints
- Update README environment variable table

The openai provider uses the existing @roo-code/types openAi schema
(openAiBaseUrl, openAiApiKey, openAiModelId) which is already fully
supported in the core extension via OpenAiHandler.

Usage:
  export OPENAI_API_KEY=sk-local
  export OPENAI_BASE_URL=http://localhost:8080/v1
  roo --provider openai --model my-model "Hello"

Closes #11917

apps/cli/README.md

@@ -215,10 +215,13 @@ The CLI will look for API keys in environment variables if not provided via `--a
 | roo               | `ROO_API_KEY`               |
 | anthropic         | `ANTHROPIC_API_KEY`         |
 | openai-native     | `OPENAI_API_KEY`            |
+| openai            | `OPENAI_API_KEY`            |
 | openrouter        | `OPENROUTER_API_KEY`        |
 | gemini            | `GOOGLE_API_KEY`            |
 | vercel-ai-gateway | `VERCEL_AI_GATEWAY_API_KEY` |
 
+The `openai` provider also reads `OPENAI_BASE_URL` to set a custom API endpoint (e.g., `http://localhost:8080/v1` for locally deployed models).
+
 **Authentication Environment Variables:**
 
 | Variable          | Description                                                          |

apps/cli/src/lib/utils/provider.ts

@@ -5,6 +5,7 @@ import type { SupportedProvider } from "@/types/index.js"
 const envVarMap: Record<SupportedProvider, string> = {
 	anthropic: "ANTHROPIC_API_KEY",
 	"openai-native": "OPENAI_API_KEY",
+	openai: "OPENAI_API_KEY",
 	gemini: "GOOGLE_API_KEY",
 	openrouter: "OPENROUTER_API_KEY",
 	"vercel-ai-gateway": "VERCEL_AI_GATEWAY_API_KEY",
@@ -36,6 +37,11 @@ export function getProviderSettings(
 			if (apiKey) config.openAiNativeApiKey = apiKey
 			if (model) config.apiModelId = model
 			break
+		case "openai":
+			if (apiKey) config.openAiApiKey = apiKey
+			if (model) config.openAiModelId = model
+			if (process.env.OPENAI_BASE_URL) config.openAiBaseUrl = process.env.OPENAI_BASE_URL
+			break
 		case "gemini":
 			if (apiKey) config.geminiApiKey = apiKey
 			if (model) config.apiModelId = model

apps/cli/src/types/types.ts

@@ -4,6 +4,7 @@ import type { OutputFormat } from "./json-events.js"
 export const supportedProviders = [
 	"anthropic",
 	"openai-native",
+	"openai",
 	"gemini",
 	"openrouter",
 	"vercel-ai-gateway",