Overhaul UI with shadcn components and new pages

Add shadcn/ui components (badge, button, card, input, select,
separator). Add company context provider. New pages: Activity,
Approvals, Companies, Costs, Org chart. Restyle existing pages
(Dashboard, Agents, Issues, Goals, Projects) with shadcn components
and dark theme. Update layout, sidebar navigation, and routing.

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

ui/src/hooks/useAgents.ts

@@ -2,7 +2,10 @@ import { useCallback } from "react";
 import { agentsApi } from "../api/agents";
 import { useApi } from "./useApi";
 
-export function useAgents() {
-  const fetcher = useCallback(() => agentsApi.list(), []);
+export function useAgents(companyId: string | null) {
+  const fetcher = useCallback(() => {
+    if (!companyId) return Promise.resolve([]);
+    return agentsApi.list(companyId);
+  }, [companyId]);
   return useApi(fetcher);
 }