Update docs and screenshots

backend/app/auth/__init__.py

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+"""Authentication services."""
+

backend/app/auth/service.py

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+from __future__ import annotations
+
+import secrets
+from dataclasses import dataclass
+from datetime import UTC, datetime, timedelta
+
+from argon2 import PasswordHasher
+
+
+@dataclass(slots=True)
+class SessionData:
+    session_id: str
+    csrf_token: str
+    expires_at: datetime
+    role: str
+    username: str
+
+
+class AuthService:
+    def __init__(self) -> None:
+        self._hasher = PasswordHasher()
+        self._sessions: dict[str, SessionData] = {}
+
+    def hash_password(self, password: str) -> str:
+        return self._hasher.hash(password)
+
+    def verify_password(self, password: str, password_hash: str) -> bool:
+        try:
+            return self._hasher.verify(password_hash, password)
+        except Exception:
+            return False
+
+    def create_session(self, username: str, role: str) -> SessionData:
+        session_id = secrets.token_hex(24)
+        csrf_token = secrets.token_hex(16)
+        expires_at = datetime.now(UTC) + timedelta(hours=12)
+        session = SessionData(
+            session_id=session_id,
+            csrf_token=csrf_token,
+            expires_at=expires_at,
+            role=role,
+            username=username,
+        )
+        self._sessions[session_id] = session
+        return session
+
+    def get_session(self, session_id: str | None) -> SessionData | None:
+        if session_id is None:
+            return None
+        session = self._sessions.get(session_id)
+        if session is None:
+            return None
+        if session.expires_at < datetime.now(UTC):
+            self._sessions.pop(session_id, None)
+            return None
+        return session
+