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/components/QuotaBar.tsx

@@ -0,0 +1,65 @@
+import { cn } from "@/lib/utils";
+
+interface QuotaBarProps {
+  label: string;
+  // value between 0 and 100
+  percentUsed: number;
+  leftLabel: string;
+  rightLabel?: string;
+  // shows a 2px destructive notch at the fill tip when true
+  showDeficitNotch?: boolean;
+  className?: string;
+}
+
+function fillColor(pct: number): string {
+  if (pct > 90) return "bg-red-400";
+  if (pct > 70) return "bg-yellow-400";
+  return "bg-green-400";
+}
+
+export function QuotaBar({
+  label,
+  percentUsed,
+  leftLabel,
+  rightLabel,
+  showDeficitNotch = false,
+  className,
+}: QuotaBarProps) {
+  const clampedPct = Math.min(100, Math.max(0, percentUsed));
+  // keep the notch visible even near the edges
+  const notchLeft = Math.min(clampedPct, 97);
+
+  return (
+    <div className={cn("space-y-1.5", className)}>
+      {/* row header */}
+      <div className="flex items-center justify-between gap-2">
+        <span className="text-xs text-muted-foreground">{label}</span>
+        <div className="flex items-center gap-2 shrink-0">
+          <span className="text-xs font-medium tabular-nums">{leftLabel}</span>
+          {rightLabel && (
+            <span className="text-xs text-muted-foreground tabular-nums">{rightLabel}</span>
+          )}
+        </div>
+      </div>
+
+      {/* track — boxed border, square corners to match the theme */}
+      <div className="relative h-2 w-full border border-border overflow-hidden">
+        {/* fill */}
+        <div
+          className={cn(
+            "absolute inset-y-0 left-0 transition-[width,background-color] duration-150",
+            fillColor(clampedPct),
+          )}
+          style={{ width: `${clampedPct}%` }}
+        />
+        {/* deficit notch — 2px wide, sits at the fill tip */}
+        {showDeficitNotch && clampedPct > 0 && (
+          <div
+            className="absolute inset-y-0 w-[2px] bg-destructive z-10"
+            style={{ left: `${notchLeft}%` }}
+          />
+        )}
+      </div>
+    </div>
+  );
+}