fix(android): unblock first device test — auth contrast + dynamic base URL

Two regressions surfaced on the first real device run.

1. Contrast on ServerUrl + Login screens: both wrapped content in a
   bare Box(fillMaxSize), no Surface. The obsidian background never
   painted (rendered against the system root view's default),
   LocalContentColor cascade fell through to Material's default
   contentColor — the screens rendered as near-invisible dark text
   on dark grey. Wrap both in Surface(color = background, contentColor
   = onBackground) so the bg paints AND the M3 contentColor pipeline
   flows correctly through OutlinedTextField labels / cursor /
   placeholders + the Button content tint.

2. The bigger bug: NetworkModule.provideRetrofit read
   authStore.baseUrl.value ONCE at Retrofit creation. AuthStore loads
   from Room async, so at injection time the value was still the
   localhost:8080 placeholder. Result: even after the user typed
   their real server URL on the ServerUrl screen, every API call
   kept hitting localhost:8080 ("Failed to connect to
   localhost/127.0.0.1:8080" on the login attempt). The pre-fix
   NetworkModule comment even acknowledged it — *"Server-URL
   changes require an app relaunch"*.

   Fix: per-request rewrite. New BaseUrlInterceptor reads the live
   AuthStore.baseUrl.value on every request and rewrites
   scheme/host/port of the outgoing URL. Retrofit now keeps a
   placeholder baseUrl ("http://placeholder.invalid/") solely to
   satisfy its parser; the actual target host is dynamic. Order in
   OkHttp chain: BaseUrl first → Auth → logging, so the cookie
   interceptor sees the final URL.

New:
  - api/BaseUrlInterceptor.kt — per-request scheme/host/port rewrite
    from AuthStore.baseUrl. Falls through to the original request
    when the stored URL is unparseable.

Modified:
  - api/NetworkModule.kt — adds BaseUrlInterceptor to the OkHttp
    chain. Drops the AuthStore dependency from provideRetrofit;
    swaps baseUrl for the placeholder.
  - auth/ui/ServerUrlScreen.kt — Box → Surface wrap.
  - auth/ui/LoginScreen.kt — Box → Surface wrap.

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

android/app/build/intermediates/incremental/packageDebug/tmp/debug/dex-renamer-state.txt

@@ -0,0 +1,61 @@
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