Teach CLI diagnose about CrossModel env auth

`codexbar diagnose` resolved no API auth for an env-only CrossModel
setup because CLIDiagnoseCommand's env-auth switch had no `.crossmodel`
case and fell through to false, even though CROSSMODEL_API_KEY is a
supported token source. Add the case and a focused diagnostic test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: hujuncheng

Sources/CodexBarCLI/CLIDiagnoseCommand.swift

@@ -225,6 +225,8 @@ extension CodexBarCLI {
             ChutesSettingsReader.apiKey(environment: environment) != nil
         case .crof:
             CrofSettingsReader.apiKey(environment: environment) != nil
+        case .crossmodel:
+            CrossModelSettingsReader.apiToken(environment: environment) != nil
         case .deepgram:
             DeepgramSettingsReader.apiKey(environment: environment) != nil
         case .deepseek:

Tests/CodexBarTests/CLIDiagnoseCommandTests.swift

@@ -115,6 +115,19 @@ struct CLIDiagnoseCommandTests {
         #expect(summary.modes == ["api"])
     }
 
+    @Test
+    func `generic diagnose auth summary detects CrossModel environment credentials`() {
+        let summary = CodexBarCLI._diagnosticAuthSummaryForTesting(
+            provider: .crossmodel,
+            account: nil,
+            config: nil,
+            environment: [CrossModelSettingsReader.envKey: "cm-test"],
+            settings: nil)
+
+        #expect(summary.configured)
+        #expect(summary.modes == ["api"])
+    }
+
     @Test
     func `generic diagnose auth summary requires complete Bedrock credentials`() {
         let partial = CodexBarCLI._diagnosticAuthSummaryForTesting(