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/config.rs

@@ -1,4 +1,2 @@
-pub struct ServerConfig {
-    pub bind_addr: String,
-    pub data_dir: String,
-}
+// Server configuration — currently handled via CLI args in main.rs.
+// This module will be used when file-based configuration is added.