Fix all compile warnings in frontend and backend

Removed unused imports, fields, methods, and structs that were generating warnings during compilation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/auth.rs

@@ -1,5 +1,5 @@
 use bcrypt::{hash, verify, DEFAULT_COST};
-use chrono::{DateTime, Duration, Utc};
+use chrono::{Duration, Utc};
 use jsonwebtoken::{decode, encode, Algorithm, DecodingKey, EncodingKey, Header, Validation};
 use serde::{Deserialize, Serialize};
 use sqlx::{Row, SqlitePool};