phase 8: lobby UI + cross-stack lobby command catalog + TS FlatBuffers

- Extend pkg/model/lobby and pkg/schema/fbs/lobby.fbs with public-games
  list, my-applications/invites lists, game-create, application-submit,
  invite-redeem/decline. Mirror the matching transcoder pairs and Go
  fixture round-trip tests.
- Wire the seven new lobby message types through
  gateway/internal/backendclient/{routes,lobby_commands}.go with
  per-command REST helpers, JSON-tolerant decoding of backend wire
  shapes, and httptest-based unit coverage for success / 4xx / 5xx /
  503 across each command.
- Introduce TS-side FlatBuffers via the `flatbuffers` runtime dep, a
  `make fbs-ts` target driving flatc, and the generated bindings under
  ui/frontend/src/proto/galaxy/fbs. Phase 7's `user.account.get` decode
  now uses these bindings as well, closing the JSON.parse vs
  FlatBuffers gap that would have failed against a real local stack.
- Replace the placeholder lobby with five sections (my games, pending
  invitations, my applications, public games, create new game) and the
  /lobby/create form. Submit-application uses an inline race-name
  form on the public-game card; create-game keeps name / description /
  turn_schedule / enrollment_ends_at always visible and the rest under
  an Advanced toggle with TS-side defaults.
- Update lobby/+page.svelte to throw LobbyError on non-ok result codes;
  GalaxyClient.executeCommand now returns { resultCode, payloadBytes }.
- Vitest binding round-trips, lobby.ts wrapper unit tests, lobby-page
  + lobby-create component tests, Playwright lobby-flow.spec covering
  create / submit / accept across all four projects. Phase 7 e2e was
  migrated to the FlatBuffers fixtures and to click+fill against the
  Safari-autofill readonly inputs.
- Mark Phase 8 done in ui/PLAN.md, mirror the wire-format note into
  Phase 7, append the new lobby commands to gateway/README.md and
  docs/ARCHITECTURE.md, add ui/docs/lobby.md.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/README.md

@@ -75,8 +75,8 @@ ui/
     ├── src/lib/             env config, session store, revocation watcher
     ├── src/platform/core/   Core interface + WasmCore adapter
     ├── src/platform/store/  KeyStore/Cache interfaces + web adapter
-    ├── src/proto/           generated Protobuf-ES + Connect descriptors
-    ├── src/routes/          SvelteKit routes (/, /login, /lobby)
+    ├── src/proto/           generated Protobuf-ES + Connect descriptors + FlatBuffers TS bindings
+    ├── src/routes/          SvelteKit routes (/, /login, /lobby, /lobby/create)
     └── static/              core.wasm + wasm_exec.js (committed artefacts)
 ```
 
@@ -84,6 +84,8 @@ Linked topic docs:
 
 - [`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
+  / invite lifecycle, create-game form defaults.
 - [`docs/i18n.md`](docs/i18n.md) — translation primitive, native-name
   language picker, recipe for adding a new locale.
 - [`docs/storage.md`](docs/storage.md) — web KeyStore/Cache,
@@ -117,14 +119,16 @@ named targets are placeholders until the named phase lands; running
 `make` with no arguments prints the current placeholder map.
 
 ```text
-make web             Vite production build           Phase 5+
-make wasm            TinyGo → core.wasm              Phase 5
-make gomobile        gomobile bind → ios + android   Phase 32+
-make desktop-mac     Wails build for darwin          Phase 31
-make desktop-win     Wails build for windows         Phase 31
-make desktop-linux   Wails build for linux           Phase 31
-make ios             Capacitor + xcodebuild          Phase 32+
-make android         Capacitor + gradle              Phase 32+
+make web             Vite production build                      Phase 5+
+make wasm            TinyGo → core.wasm                         Phase 5
+make ts-protos       Connect-ES + Protobuf-ES gen               Phase 5
+make fbs-ts          FlatBuffers TS bindings via flatc          Phase 8
+make gomobile        gomobile bind → ios + android              Phase 32+
+make desktop-mac     Wails build for darwin                     Phase 31
+make desktop-win     Wails build for windows                    Phase 31
+make desktop-linux   Wails build for linux                      Phase 31
+make ios             Capacitor + xcodebuild                     Phase 32+
+make android         Capacitor + gradle                         Phase 32+
 make all             every target above
 ```