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/README.md

@@ -53,9 +53,15 @@ quick orientation; deeper design notes live under `ui/docs/`.
   + SQLite on desktop, iOS Keychain / Android Keystore + SQLite on
   mobile, all behind a single `KeyStore` and `Cache` TypeScript
   interface.
-- **Mobile-first navigation:** one active view occupies the main area
-  at a time; the sidebar holds a single tool (calculator, inspector,
-  or order) with persistent state on switch.
+- **Single-URL app-shell navigation:** the game UI is one route served
+  at `/game/`; the screen (login / lobby / game) and the in-game view
+  are in-memory state (`lib/app-nav.svelte.ts`), not URLs, so the
+  address bar never changes. Browser Back/Forward move between screens
+  via shallow routing without touching the URL — a model that also
+  suits the bundled standalone targets (Wails / Capacitor) that have no
+  URLs. One active view occupies the main area at a time; the sidebar
+  holds a single tool (calculator, inspector, or order) with persistent
+  state on switch. See [`docs/navigation.md`](docs/navigation.md).
 
 ## Repository layout
 
@@ -81,16 +87,18 @@ ui/
 ├── mobile/                  Capacitor project (planned — see ROADMAP.md)
 └── frontend/                SvelteKit / Vite source
     ├── src/api/             GalaxyClient + typed Connect client + auth + session
-    ├── src/lib/             env config, session store, revocation watcher
+    ├── src/lib/             app-shell nav + screens + game shell, env config, session store, stores
     ├── src/platform/core/   Core interface + WasmCore adapter
     ├── src/platform/store/  KeyStore/Cache interfaces + web adapter
     ├── src/proto/           generated Protobuf-ES + Connect descriptors + FlatBuffers TS bindings
-    ├── src/routes/          SvelteKit routes (/, /login, /lobby, /lobby/create)
+    ├── src/routes/          single-URL app-shell: `/game/` dispatcher (+page.svelte) + `/__debug/*`
     └── static/              core.wasm + wasm_exec.js (built by `make wasm` / CI; gitignored)
 ```
 
 Linked topic docs:
 
+- [`docs/navigation.md`](docs/navigation.md) — single-URL app-shell,
+  screens and views as in-memory state, screen history, sidebar tools.
 - [`docs/auth-flow.md`](docs/auth-flow.md) — email-code login,
   session store state machine, revocation watcher.
 - [`docs/lobby.md`](docs/lobby.md) — lobby UI sections, application