feat: add local OneNote and ONEPKG reader

src/components/HelpDialog.tsx

@@ -0,0 +1,37 @@
+interface HelpDialogProps {
+  onClose(): void;
+}
+
+export function HelpDialog({ onClose }: HelpDialogProps) {
+  return (
+    <div className="dialog-backdrop">
+      <section
+        className="help-dialog"
+        role="dialog"
+        aria-modal="true"
+        aria-labelledby="help-title"
+      >
+        <h2 id="help-title">About OneNote Tools</h2>
+        <p>
+          Read the tested desktop revision-store .one subset and single-cabinet
+          LZX or uncompressed .onepkg packages with a native TypeScript parser.
+          Unsupported content remains visible as diagnostics instead of being
+          silently discarded.
+        </p>
+        <p>
+          FSSHTTP sections, MSZIP and Quantum packages, multi-cabinet archives,
+          notebook TOC ordering, visual fidelity, attachments, and export are
+          not supported in this release.
+        </p>
+        <p>
+          Nothing is uploaded, persisted, or sent to telemetry. Closing or
+          clearing releases application references and terminates the worker;
+          this is not a secure-erasure guarantee.
+        </p>
+        <button type="button" onClick={onClose}>
+          Close
+        </button>
+      </section>
+    </div>
+  );
+}