feat: add Mascot component with state-driven SVG rendering

Implement the <Mascot> component that renders Nori in four emotional
states (idle, sleeping, excited, lonely) with distinct SVG geometry,
color palettes, and facial expressions. Includes useMascotAnimation
hook stub for Task 2 and full test coverage (15 tests).

packages/web/src/hooks/useMascotAnimation.ts

@@ -0,0 +1,14 @@
+import type { RefObject } from 'react';
+import type { MascotState } from '../components/ui/Mascot';
+
+/**
+ * Drives Mascot SVG animations (idle bob, sleeping breathe, etc.).
+ * Stub — real implementation comes in Task 2.
+ */
+export function useMascotAnimation(
+  _svgRef: RefObject<SVGSVGElement | null>,
+  _containerRef: RefObject<HTMLDivElement | null>,
+  _state: MascotState,
+): void {
+  // Task 2 implements animation logic
+}