Add user management system with JWT authentication

- Database schema: users, permissions, client_access tables
- Auth: JWT tokens with Argon2 password hashing
- API: login, user CRUD, permission management
- Dashboard: login required, admin Users tab
- Auto-creates initial admin user on first run

server/src/auth/password.rs

@@ -0,0 +1,57 @@
+//! Password hashing using Argon2id
+
+use anyhow::{anyhow, Result};
+use argon2::{
+    password_hash::{rand_core::OsRng, PasswordHash, PasswordHasher, PasswordVerifier, SaltString},
+    Argon2,
+};
+
+/// Hash a password using Argon2id
+pub fn hash_password(password: &str) -> Result<String> {
+    let salt = SaltString::generate(&mut OsRng);
+    let argon2 = Argon2::default();
+    let hash = argon2
+        .hash_password(password.as_bytes(), &salt)
+        .map_err(|e| anyhow!("Failed to hash password: {}", e))?;
+    Ok(hash.to_string())
+}
+
+/// Verify a password against a stored hash
+pub fn verify_password(password: &str, hash: &str) -> Result<bool> {
+    let parsed_hash = PasswordHash::new(hash)
+        .map_err(|e| anyhow!("Invalid password hash format: {}", e))?;
+    let argon2 = Argon2::default();
+    Ok(argon2.verify_password(password.as_bytes(), &parsed_hash).is_ok())
+}
+
+/// Generate a random password (for initial admin)
+pub fn generate_random_password(length: usize) -> String {
+    use rand::Rng;
+    const CHARSET: &[u8] = b"ABCDEFGHJKLMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz23456789!@#$%";
+    let mut rng = rand::thread_rng();
+    (0..length)
+        .map(|_| {
+            let idx = rng.gen_range(0..CHARSET.len());
+            CHARSET[idx] as char
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_hash_and_verify() {
+        let password = "test_password_123";
+        let hash = hash_password(password).unwrap();
+        assert!(verify_password(password, &hash).unwrap());
+        assert!(!verify_password("wrong_password", &hash).unwrap());
+    }
+
+    #[test]
+    fn test_random_password() {
+        let password = generate_random_password(16);
+        assert_eq!(password.len(), 16);
+    }
+}