feat(ui): lobby site-style sidebar + profile screen (#47)

- Wrap lobby and profile in a shared `lobby-shell.svelte` chrome:
  page-list sidebar (Overview/Profile) and a top "Player-xxxx"
  identity strip mirroring the project site's monospace look.
- Strip the legacy `lobby.title`, device-session-id `<code>`, and
  `lobby.greeting` paragraph; the identity strip both names the user
  and opens the profile editor.
- Add a top-level `profile` AppScreen with a three-field form
  (`display_name`, `preferred_language`, `time_zone`) backed by a new
  `src/api/account.ts` wrapper around `user.account.get`,
  `user.profile.update`, and `user.settings.update`. Saving switches
  the active i18n locale in-place when the new preferred language is
  one the UI ships translations for.
- Update e2e fixture + auth-flow / lobby-flow specs to use the new
  `lobby-account-name` testid and wait for the loaded identity before
  releasing pending `SubscribeEvents` (webkit revocation race). New
  `profile-screen.spec.ts` covers navigation, edit-save, and cancel.
- Sync `ui/docs/lobby.md` and `ui/docs/navigation.md` to the new
  layout.

Closes #47

ui/docs/lobby.md

@@ -2,16 +2,36 @@
 
 The lobby is the first authenticated view; the user lands here after
 the email-code login completes (see
-[`docs/auth-flow.md`](auth-flow.md)). This doc captures the
-sections, the application / invite lifecycle the user sees, and
-the defaults baked into the create-game form.
+[`docs/auth-flow.md`](auth-flow.md)). This doc captures the shared
+shell, the Overview sections, the profile sub-screen, and the
+defaults baked into the create-game form.
 
-## Sections
+## Shell
 
-The lobby renders one column of sections, top to bottom, with the
-common content max-width capped at `32rem` (same convention as the
-login page). Cards inside each section take the full available
-width.
+Lobby and profile share a single chrome implemented in
+`lib/screens/lobby-shell.svelte`. The chrome mirrors the project
+site's VitePress layout: a left page-list sidebar (Overview /
+Profile), a top identity strip on the right, and the page content in
+the right-hand column. The shell uses `var(--font-mono)` so the
+post-login pages adopt the "nerdy" type stack that the public site
+already uses.
+
+The identity strip renders the caller's `display_name` (falling back
+to the immutable `user_name` handle, then to a loading placeholder
+while `user.account.get` resolves) as a `data-testid="lobby-account-name"`
+button. Clicking it switches the top-level screen to `profile`
+(`appScreen.go("profile")`); the e2e suites use that testid as their
+lobby-loaded signal. The logout button sits next to it
+(`session.signOut("user")`).
+
+The sidebar always renders both pages; clicking the active page is a
+no-op. The shell collapses to a horizontal scrolling strip below
+640px.
+
+## Overview sections
+
+The Overview page renders one column of sections, top to bottom.
+Cards inside each section take the full available width.
 
 | Section              | Empty state           | Source                     | Action                                                    |
 | -------------------- | --------------------- | -------------------------- | --------------------------------------------------------- |
@@ -21,9 +41,30 @@ width.
 | `my applications`    | `no applications`     | `lobby.my.applications.list` | Status badge (`pending` / `approved` / `rejected`)      |
 | `public games`       | `no public games`     | `lobby.public.games.list`  | Submit application via inline race-name form (`lobby.application.submit`) |
 
-The header preserves the device-session-id `<code>` block (kept as
-a debug affordance) plus a greeting if the gateway returns a
-`display_name` for the caller.
+## Profile sub-screen
+
+`lib/screens/profile-screen.svelte` is a top-level `AppScreen` (peer of
+`lobby` and `lobby-create`). The browser Back stack treats it the
+same as the create screen — pushing a fresh history entry on entry,
+falling back to lobby on Back/Forward (see
+[`navigation.md`](navigation.md)).
+
+On mount it issues `user.account.get` through `src/api/account.ts`
+and renders an identity read-out (immutable `user_name`, `email`)
+plus a three-field form:
+
+| Field                 | Endpoint              | Notes                                                          |
+| --------------------- | --------------------- | -------------------------------------------------------------- |
+| `display_name`        | `user.profile.update` | Trimmed; empty value clears the stored name (backend PATCH semantics). |
+| `preferred_language`  | `user.settings.update`| `<select>` over `SUPPORTED_LOCALES`; if the stored value is unsupported the option is preserved verbatim so a round-trip save does not silently switch it. |
+| `time_zone`           | `user.settings.update`| Free-text IANA name. Placeholder shows the browser's current zone; backend validates with `time.LoadLocation`. |
+
+Save fires `user.profile.update` and/or `user.settings.update`
+conditionally on which fields actually changed, then returns to the
+lobby (`appScreen.go("lobby")`). When the saved
+`preferred_language` is one the UI also ships translations for, the
+active i18n locale switches in-place so the rest of the session
+matches the new preference.
 
 `GameSummary` carries a `current_turn` field that the lobby UI does
 not display directly — the in-game shell reads it from the same