feat: add Vercel AI Gateway as a provider

Adds 'vercel' as a recognized provider throughout the model resolution
system, enabling users with Vercel AI Gateway to use it as a universal
fallback for OpenAI, Anthropic, and Google models.

The gateway transform infers the sub-provider from canonical model names
(claude->anthropic, gpt->openai, gemini->google) and delegates to the
appropriate provider-specific transform, producing model strings like
vercel/anthropic/claude-opus-4.6.

src/cli/config-manager/detect-current-config.ts

@@ -12,6 +12,7 @@ function detectProvidersFromOmoConfig(): {
   hasZaiCodingPlan: boolean
   hasKimiForCoding: boolean
   hasOpencodeGo: boolean
+  hasVercelAiGateway: boolean
 } {
   const omoConfigPath = getOmoConfigPath()
   if (!existsSync(omoConfigPath)) {
@@ -21,6 +22,7 @@ function detectProvidersFromOmoConfig(): {
       hasZaiCodingPlan: false,
       hasKimiForCoding: false,
       hasOpencodeGo: false,
+      hasVercelAiGateway: false,
     }
   }
 
@@ -34,6 +36,7 @@ function detectProvidersFromOmoConfig(): {
         hasZaiCodingPlan: false,
         hasKimiForCoding: false,
         hasOpencodeGo: false,
+        hasVercelAiGateway: false,
       }
     }
 
@@ -43,8 +46,9 @@ function detectProvidersFromOmoConfig(): {
     const hasZaiCodingPlan = configStr.includes('"zai-coding-plan/')
     const hasKimiForCoding = configStr.includes('"kimi-for-coding/')
     const hasOpencodeGo = configStr.includes('"opencode-go/')
+    const hasVercelAiGateway = configStr.includes('"vercel/')
 
-    return { hasOpenAI, hasOpencodeZen, hasZaiCodingPlan, hasKimiForCoding, hasOpencodeGo }
+    return { hasOpenAI, hasOpencodeZen, hasZaiCodingPlan, hasKimiForCoding, hasOpencodeGo, hasVercelAiGateway }
   } catch {
     return {
       hasOpenAI: true,
@@ -52,6 +56,7 @@ function detectProvidersFromOmoConfig(): {
       hasZaiCodingPlan: false,
       hasKimiForCoding: false,
       hasOpencodeGo: false,
+      hasVercelAiGateway: false,
     }
   }
 }
@@ -78,6 +83,7 @@ export function detectCurrentConfig(): DetectedConfig {
     hasZaiCodingPlan: false,
     hasKimiForCoding: false,
     hasOpencodeGo: false,
+    hasVercelAiGateway: false,
   }
 
   const { format, path } = detectConfigFormat()
@@ -106,12 +112,13 @@ export function detectCurrentConfig(): DetectedConfig {
   const providers = openCodeConfig.provider as Record<string, unknown> | undefined
   result.hasGemini = providers ? "google" in providers : false
 
-  const { hasOpenAI, hasOpencodeZen, hasZaiCodingPlan, hasKimiForCoding, hasOpencodeGo } = detectProvidersFromOmoConfig()
+  const { hasOpenAI, hasOpencodeZen, hasZaiCodingPlan, hasKimiForCoding, hasOpencodeGo, hasVercelAiGateway } = detectProvidersFromOmoConfig()
   result.hasOpenAI = hasOpenAI
   result.hasOpencodeZen = hasOpencodeZen
   result.hasZaiCodingPlan = hasZaiCodingPlan
   result.hasKimiForCoding = hasKimiForCoding
   result.hasOpencodeGo = hasOpencodeGo
+  result.hasVercelAiGateway = hasVercelAiGateway
 
   return result
 }