Fix all compiler warnings across server and client

- Remove unused ServerConfig struct (config via CLI args)
- Remove unused otpks field from Database (not yet needed)
- Wire AppError into message routes with proper error propagation
- Remove unused imports in send.rs (Seed, MessageContent, etc.)
- Suppress dead_code on BundleResponse.fingerprint (needed by serde)

Zero warnings, 17/17 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/crates/warzone-server/src/errors.rs

@@ -1,10 +1,12 @@
 use axum::http::StatusCode;
 use axum::response::{IntoResponse, Response};
 
+/// Wraps anyhow::Error into an axum-compatible error response.
 pub struct AppError(pub anyhow::Error);
 
 impl IntoResponse for AppError {
     fn into_response(self) -> Response {
+        tracing::error!("{:#}", self.0);
         (StatusCode::INTERNAL_SERVER_ERROR, self.0.to_string()).into_response()
     }
 }
@@ -14,3 +16,6 @@ impl<E: Into<anyhow::Error>> From<E> for AppError {
         AppError(err.into())
     }
 }
+
+/// Convenience type for route handlers.
+pub type AppResult<T> = Result<T, AppError>;