feat(02-03): install Schedule-X stack + CSS token layer + main.tsx imports

- Install @schedule-x/{calendar,react,theme-default,event-modal,events-service}@4.x
- Install temporal-polyfill@0.3.2 and lucide-react@1.17.0
- Create src/styles/tokens.css: all color/spacing/typography/breakpoint tokens
  plus --sx-color-* Schedule-X overrides mapped to project tokens
- Create src/styles/tokens.ts: TypeScript mirror of token values for inline styles
- Create src/styles/index.css: imports tokens.css + minimal global reset
- Update main.tsx: Temporal polyfill first, then SX theme CSS, then styles/index.css

apps/pwa/src/styles/index.css

@@ -0,0 +1,29 @@
+/**
+ * FamilySync global styles entry point.
+ *
+ * Import order matters — tokens.css must be imported AFTER
+ * @schedule-x/theme-default/dist/index.css (handled in main.tsx)
+ * so the --sx-color-* overrides win the cascade.
+ */
+
+@import './tokens.css';
+
+/* ── Minimal Global Reset ─────────────────────────────────────────────────── */
+
+*,
+*::before,
+*::after {
+  box-sizing: border-box;
+}
+
+body {
+  margin: 0;
+  font-family: var(--font-family-base);
+  font-size: var(--text-body-size);
+  font-weight: var(--text-body-weight);
+  line-height: var(--text-body-line-height);
+  color: var(--color-text-primary);
+  background-color: var(--color-surface);
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}