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-client/src/net.rs

@@ -23,6 +23,7 @@ struct SendRequest {
 }
 
 #[derive(Deserialize)]
+#[allow(dead_code)]
 struct BundleResponse {
     fingerprint: String,
     bundle: String, // base64