Add presence indicators and a manual "appear offline" override (#36)

Every avatar in the app (chat messages, room member list, your own
avatar in the top bar/profile, the admin user list, the room-invite
search) now shows a green/red presence dot. Also adds a global
"Appear offline" toggle in the account menu, letting a user lurk in a
room undetected -- it overrides the real connection state everywhere,
not per-room.

Backend: new GlobalPresence (backend/app/ws/global_presence.py), a
cross-instance Redis-backed connection tracker parallel to the
existing per-room Presence, incremented/decremented on WS connect/
disconnect. A new users.appear_offline column (migration
f0f6e494454a) always wins over actual connection state when computing
displayed status. RoomMemberRead gained a computed `status` field;
add_member/change_member_role/list_room_members all compute it via a
shared _member_status() helper. Connect/disconnect and profile
updates (display_name, avatar, appear_offline) all broadcast
member_updated to every room the user belongs to, reusing the
broadcast infrastructure from the earlier avatar-staleness fix, so
chat surfaces update live with no new WS envelope type needed. A new
GET /api/users/online gives the admin list and user-search a snapshot
(deliberately not live -- see backend/app/routers/users.py) for
surfaces where "accurate as of page load" is good enough.

Frontend: UserAvatar renders an optional status dot; every call site
threads status/appear_offline through from whichever data source it
already has (room members, the current user, or the new online-ids
snapshot for admin/search).

4 new backend tests (backend/tests/test_presence.py); existing
broadcast-adjacent WS tests updated to tolerate the new member_updated
noise on connect. Verified end-to-end in the browser with two real
users: presence dot flips live on connect/disconnect via the existing
room-broadcast channel, and the lurk toggle correctly forces offline
while still connected.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/tests/test_presence.py

@@ -0,0 +1,132 @@
+import uuid
+
+from app.schemas.user import UserCreate
+from app.services.auth_service import register_user
+
+# Disconnect-side cleanup (GlobalPresence.disconnect, the offline broadcast)
+# is deliberately not exercised end-to-end here via a `with websocket_
+# connect(...)` block closing: Starlette's TestClient tears down a
+# websocket session by cancelling the server-side handler's task (confirmed
+# via asyncio.CancelledError while investigating a hang here), not by
+# delivering a real ASGI "websocket.disconnect" message the way an actual
+# client going away does -- so a `finally` block's own `await` calls can be
+# interrupted mid-cleanup in tests without that ever happening in
+# production. No existing test in this suite exercises presence.leave()
+# post-disconnect either, for the same reason. The connect-side behavior
+# below (the half that's actually reliably testable) is what matters most:
+# it proves the online transition and its broadcast work correctly.
+
+
+def _unique(prefix: str) -> str:
+    return f"{prefix}-{uuid.uuid4().hex[:8]}"
+
+
+def _register_ws(ws_client, username: str) -> dict:
+    async def _seed():
+        async with ws_client.session_factory() as session:
+            await register_user(
+                session,
+                UserCreate(username=username, email=f"{username}@example.com", password="password123"),
+            )
+
+    ws_client.portal.call(_seed)
+    resp = ws_client.post(
+        "/api/auth/login", json={"username_or_email": username, "password": "password123"}
+    )
+    assert resp.status_code == 200, resp.text
+    return resp.json()
+
+
+def test_member_status_reflects_connection(ws_client):
+    alice = _register_ws(ws_client, _unique("alice"))
+    room = ws_client.post("/api/rooms", json={"name": _unique("general")}).json()
+
+    members = ws_client.get(f"/api/rooms/{room['id']}/members").json()
+    assert members[0]["status"] == "offline"
+
+    with ws_client.websocket_connect("/ws/chat") as ws:
+        ws.send_json({"type": "join", "room_id": room["id"]})
+        assert ws.receive_json()["type"] == "joined"
+
+        members = ws_client.get(f"/api/rooms/{room['id']}/members").json()
+        assert members[0]["status"] == "online"
+
+
+def test_connect_broadcasts_presence_to_shared_room(ws_client):
+    alice = _register_ws(ws_client, _unique("alice"))
+    room = ws_client.post("/api/rooms", json={"name": _unique("general")}).json()
+
+    bob = _register_ws(ws_client, _unique("bob"))
+    ws_client.post(f"/api/rooms/{room['id']}/join")
+
+    ws_client.post(
+        "/api/auth/login", json={"username_or_email": alice["username"], "password": "password123"}
+    )
+    with ws_client.websocket_connect("/ws/chat") as alice_ws:
+        alice_ws.send_json({"type": "join", "room_id": room["id"]})
+        assert alice_ws.receive_json()["type"] == "joined"
+
+        ws_client.post(
+            "/api/auth/login", json={"username_or_email": bob["username"], "password": "password123"}
+        )
+        with ws_client.websocket_connect("/ws/chat"):
+            # bob connecting is a genuine offline->online transition for
+            # him -- alice, already joined, should hear about it even
+            # though she never sent anything and bob never joined a room.
+            assert alice_ws.receive_json() == {
+                "type": "member_updated",
+                "room_id": room["id"],
+                "user_id": bob["id"],
+            }
+
+
+def test_appear_offline_overrides_actual_connection(ws_client):
+    alice = _register_ws(ws_client, _unique("alice"))
+    room = ws_client.post("/api/rooms", json={"name": _unique("general")}).json()
+
+    with ws_client.websocket_connect("/ws/chat") as ws:
+        ws.send_json({"type": "join", "room_id": room["id"]})
+        assert ws.receive_json()["type"] == "joined"
+
+        members = ws_client.get(f"/api/rooms/{room['id']}/members").json()
+        assert members[0]["status"] == "online"
+
+        resp = ws_client.patch("/api/auth/me", json={"appear_offline": True})
+        assert resp.status_code == 200
+        assert resp.json()["appear_offline"] is True
+
+        # alice is joined to her own room, so the broadcast her own change
+        # triggers reaches her own socket.
+        assert ws.receive_json() == {"type": "member_updated", "room_id": room["id"], "user_id": alice["id"]}
+
+        members = ws_client.get(f"/api/rooms/{room['id']}/members").json()
+        assert members[0]["status"] == "offline"
+
+        resp = ws_client.patch("/api/auth/me", json={"appear_offline": False})
+        assert resp.status_code == 200
+        assert ws.receive_json()["type"] == "member_updated"
+
+        members = ws_client.get(f"/api/rooms/{room['id']}/members").json()
+        assert members[0]["status"] == "online"
+
+
+def test_online_users_endpoint_respects_appear_offline(ws_client):
+    alice = _register_ws(ws_client, _unique("alice"))
+    bob = _register_ws(ws_client, _unique("bob"))
+
+    ws_client.post(
+        "/api/auth/login", json={"username_or_email": alice["username"], "password": "password123"}
+    )
+    with ws_client.websocket_connect("/ws/chat"):
+        online = ws_client.get("/api/users/online").json()
+        assert alice["id"] in online
+        assert bob["id"] not in online
+
+        resp = ws_client.patch("/api/auth/me", json={"appear_offline": True})
+        assert resp.status_code == 200
+
+        online = ws_client.get("/api/users/online").json()
+        assert alice["id"] not in online
+
+    online = ws_client.get("/api/users/online").json()
+    assert alice["id"] not in online