feat(ui): add resource and usage dashboard (/usage route)

adds a new /usage page that lets board operators see how much each ai
provider is consuming across any date window, with per-model breakdowns,
rolling 5h/24h/7d burn windows, weekly budget bars, and a deficit notch
when projected spend is on track to exceed the monthly budget.

- new GET /companies/:id/costs/by-provider endpoint aggregates cost events
  by provider + model with pro-rated billing type splits from heartbeat runs
- new GET /companies/:id/costs/window-spend endpoint returns rolling window
  spend (5h, 24h, 7d) per provider with no schema changes
- QuotaBar: reusable boxed-border progress bar with green/yellow/red
  threshold fill colors and optional deficit notch
- ProviderQuotaCard: per-provider card showing budget allocation bars,
  rolling windows, subscription usage, and model breakdown with token/cost
  share overlays
- Usage page: date preset toggles (mtd, 7d, 30d, ytd, all, custom),
  provider tabs, 30s polling plus ws invalidation on cost_event
- custom date range blocks queries until both dates are selected and
  treats boundaries as local-time (not utc midnight) so full days are
  included regardless of timezone
- query key to timestamp is floored to the nearest minute to prevent
  cache churn on every 30s refetch tick

ui/src/lib/company-routes.ts

@@ -9,6 +9,7 @@ const BOARD_ROUTE_ROOTS = new Set([
   "goals",
   "approvals",
   "costs",
+  "usage",
   "activity",
   "inbox",
   "design-guide",

ui/src/lib/queryKeys.ts

@@ -71,6 +71,10 @@ export const queryKeys = {
   activity: (companyId: string) => ["activity", companyId] as const,
   costs: (companyId: string, from?: string, to?: string) =>
     ["costs", companyId, from, to] as const,
+  usageByProvider: (companyId: string, from?: string, to?: string) =>
+    ["usage-by-provider", companyId, from, to] as const,
+  usageWindowSpend: (companyId: string) =>
+    ["usage-window-spend", companyId] as const,
   heartbeats: (companyId: string, agentId?: string) =>
     ["heartbeats", companyId, agentId] as const,
   runDetail: (runId: string) => ["heartbeat-run", runId] as const,