docs(ui): sync docs to the app-shell; fix stale nav comments

Rewrite ui/docs (navigation, order-composer, auth-flow, pwa-strategy,
game-state + secondary topic docs) and ui/README for the single-URL
app-shell (in-memory screens/views, Back→lobby via shallow routing,
sessionStorage restore + validation, return-to-lobby). ui/PLAN.md gets a
Phase-10 supersede note (implemented; standalone-compatible). Fix stale
code comments (session-store auth gate, report-sections spec contract).

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

ui/frontend/tests/e2e/report-sections.spec.ts

@@ -6,10 +6,8 @@
 //   1. Every TOC anchor click scrolls the matching section into view
 //      and the section is present in the DOM with at least one row
 //      (or its empty-state copy when it is intentionally empty).
-//   2. Snapshot save/restore on the active-view-host scroll
-//      container survives a /map navigation round-trip.
-//   3. The "back to map" button navigates to the map URL.
-//   4. The mobile <select> fallback scrolls a section into view on
+//   2. The "back to map" button switches to the map view.
+//   3. The mobile <select> fallback scrolls a section into view on
 //      a narrow viewport.
 
 import { fromJson, type JsonValue } from "@bufbuild/protobuf";