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/db.rs

@@ -3,7 +3,6 @@ use anyhow::Result;
 pub struct Database {
     pub keys: sled::Tree,
     pub messages: sled::Tree,
-    pub otpks: sled::Tree,
     _db: sled::Db,
 }
 
@@ -12,11 +11,9 @@ impl Database {
         let db = sled::open(data_dir)?;
         let keys = db.open_tree("keys")?;
         let messages = db.open_tree("messages")?;
-        let otpks = db.open_tree("otpks")?;
         Ok(Database {
             keys,
             messages,
-            otpks,
             _db: db,
         })
     }