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/api/costs.ts

@@ -0,0 +1,18 @@
+import type { CostSummary } from "@paperclip/shared";
+import { api } from "./client";
+
+export interface CostByEntity {
+  agentId?: string | null;
+  projectId?: string | null;
+  costCents: number;
+  inputTokens: number;
+  outputTokens: number;
+}
+
+export const costsApi = {
+  summary: (companyId: string) => api.get<CostSummary>(`/companies/${companyId}/costs/summary`),
+  byAgent: (companyId: string) =>
+    api.get<CostByEntity[]>(`/companies/${companyId}/costs/by-agent`),
+  byProject: (companyId: string) =>
+    api.get<CostByEntity[]>(`/companies/${companyId}/costs/by-project`),
+};