Add onboarding wizard and revamp agent creation flow

Add OnboardingWizard component for first-time company setup. Rework
NewAgentDialog into a multi-step wizard with adapter selection and
config. Add server route for agent connection string generation.
Wire onboarding into Dashboard and Layout. Update DialogContext with
onboarding state.

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

ui/src/pages/Agents.tsx

@@ -118,7 +118,7 @@ export function Agents() {
       {agents && agents.length === 0 && (
         <EmptyState
           icon={Bot}
-          message="No agents yet."
+          message="Create your first agent to get started."
           action="New Agent"
           onAction={openNewAgent}
         />

ui/src/pages/Dashboard.tsx

@@ -6,6 +6,7 @@ import { activityApi } from "../api/activity";
 import { issuesApi } from "../api/issues";
 import { agentsApi } from "../api/agents";
 import { useCompany } from "../context/CompanyContext";
+import { useDialog } from "../context/DialogContext";
 import { useBreadcrumbs } from "../context/BreadcrumbContext";
 import { queryKeys } from "../lib/queryKeys";
 import { MetricCard } from "../components/MetricCard";
@@ -54,7 +55,8 @@ function getStaleIssues(issues: Issue[]): Issue[] {
 }
 
 export function Dashboard() {
-  const { selectedCompanyId, selectedCompany } = useCompany();
+  const { selectedCompanyId, selectedCompany, companies } = useCompany();
+  const { openOnboarding } = useDialog();
   const { setBreadcrumbs } = useBreadcrumbs();
   const navigate = useNavigate();
 
@@ -94,6 +96,16 @@ export function Dashboard() {
   };
 
   if (!selectedCompanyId) {
+    if (companies.length === 0) {
+      return (
+        <EmptyState
+          icon={LayoutDashboard}
+          message="Welcome to Paperclip. Set up your first company and agent to get started."
+          action="Get Started"
+          onAction={openOnboarding}
+        />
+      );
+    }
     return (
       <EmptyState icon={LayoutDashboard} message="Create or select a company to view the dashboard." />
     );