feat(auth): sessions module + permissions matrix + rate limiter

SQLite drops tzinfo on DateTime roundtrip — normalize on read/write
so callers see tz-aware datetimes.

backend/tests/test_auth_sessions.py

@@ -0,0 +1,86 @@
+"""Unit tests for cyclone.auth.sessions — Session create/validate/expire/touch."""
+
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+
+import pytest
+from sqlalchemy import delete
+
+from cyclone.auth import sessions, users
+from cyclone.db import Session as DbSession
+from cyclone.db import SessionLocal, User
+
+
+@pytest.fixture(autouse=True)
+def _clear():
+    with SessionLocal()() as db:
+        db.execute(delete(DbSession))
+        db.execute(delete(User))
+        db.commit()
+    yield
+    with SessionLocal()() as db:
+        db.execute(delete(DbSession))
+        db.execute(delete(User))
+        db.commit()
+
+
+def _make_user():
+    with SessionLocal()() as db:
+        return users.create(db, username="sessuser", password="hunter2hunter2", role="user")
+
+
+def test_create_session_returns_id_and_session():
+    user = _make_user()
+    with SessionLocal()() as db:
+        sid, sess = sessions.create(db, user_id=user.id)
+    assert len(sid) >= 32
+    assert sess.user_id == user.id
+    assert sess.expires_at > datetime.now(timezone.utc)
+
+
+def test_get_valid_returns_session_for_active():
+    user = _make_user()
+    with SessionLocal()() as db:
+        sid, _ = sessions.create(db, user_id=user.id)
+    with SessionLocal()() as db:
+        got = sessions.get_valid(db, sid)
+    assert got is not None
+    assert got.user_id == user.id
+
+
+def test_get_valid_returns_none_for_missing():
+    with SessionLocal()() as db:
+        assert sessions.get_valid(db, "does-not-exist") is None
+
+
+def test_get_valid_returns_none_for_expired():
+    user = _make_user()
+    with SessionLocal()() as db:
+        sid, _ = sessions.create(db, user_id=user.id)
+    with SessionLocal()() as db:
+        sess = sessions.get_valid(db, sid)
+        sess.expires_at = datetime.now(timezone.utc) - timedelta(seconds=1)
+        db.commit()
+    with SessionLocal()() as db:
+        assert sessions.get_valid(db, sid) is None
+
+
+def test_delete_removes_session():
+    user = _make_user()
+    with SessionLocal()() as db:
+        sid, _ = sessions.create(db, user_id=user.id)
+        sessions.delete(db, sid)
+    with SessionLocal()() as db:
+        assert sessions.get_valid(db, sid) is None
+
+
+def test_touch_extends_expiry():
+    user = _make_user()
+    with SessionLocal()() as db:
+        sid, sess = sessions.create(db, user_id=user.id)
+        original_expiry = sess.expires_at
+        sessions.touch(db, sid)
+    with SessionLocal()() as db:
+        refreshed = sessions.get_valid(db, sid)
+    assert refreshed.expires_at >= original_expiry