Add DeepSeek TUI to the ACP catalog (#1096)

* Consolidate provider selection handling

* List DeepSeek TUI in docs and website

packages/app/src/screens/workspace/workspace-draft-agent-tab-core.ts

@@ -1,3 +1,5 @@
+import { resolveSubmissionReadiness } from "@/provider-selection/provider-selection";
+
 export interface WorkspaceDraftAutoSubmitConfig {
   provider: string;
   model: string | null;
@@ -25,27 +27,19 @@ export function validateDraftSubmission(input: {
     workspaceDirectory,
     hasClient,
   } = input;
-  if (!allowsEmptyAutoSubmit && !text.trim()) {
-    return "Initial prompt is required";
-  }
-  if (composerState.providerDefinitions.length === 0) {
-    return "No available providers on the selected host";
-  }
-  if (!(autoSubmitConfig?.provider ?? composerState.selectedProvider)) {
-    return "Select a model";
-  }
-  if (composerState.isModelLoading) {
-    return "Model defaults are still loading";
-  }
-  const hasSelectedModel = Boolean(autoSubmitConfig?.model ?? composerState.effectiveModelId);
-  if (!hasSelectedModel && composerState.availableModels.length > 0) {
-    return "No model is available for the selected provider";
-  }
-  if (!workspaceDirectory) {
-    return "Workspace directory not found";
-  }
-  if (!hasClient) {
-    return "Host is not connected";
-  }
-  return null;
+  const readiness = resolveSubmissionReadiness({
+    text,
+    allowsEmptyAutoSubmit,
+    providerCount: composerState.providerDefinitions.length,
+    selection: {
+      provider: composerState.selectedProvider,
+      modelId: composerState.effectiveModelId ?? "",
+      availableModels: composerState.availableModels,
+      isModelLoading: composerState.isModelLoading,
+    },
+    autoSubmitConfig,
+    workspaceDirectory,
+    hasClient,
+  });
+  return readiness.ok ? null : (readiness.reason ?? null);
 }