chore(orbit): help modal with 9-section walk-through

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/store/helpModalStore.ts

@@ -0,0 +1,19 @@
+import { create } from 'zustand';
+
+interface HelpModalStore {
+  isOpen: boolean;
+  open: () => void;
+  close: () => void;
+}
+
+/**
+ * App-wide toggle for the Orbit help modal. Two triggers — the launch
+ * popover "How does this work?" entry and the in-session bar help button
+ * — write to the same store so they share the one rendered modal. Not
+ * persisted; resets to closed on reload.
+ */
+export const useHelpModalStore = create<HelpModalStore>(set => ({
+  isOpen: false,
+  open: () => set({ isOpen: true }),
+  close: () => set({ isOpen: false }),
+}));