Add scheduled dispatch support (edit + authoritative view)

Editing (game port, OpenTTDClient): a core of JGRPP's scheduled dispatch
DoCommands — set_scheduled_dispatch (enable/disable), add/remove schedule,
add/remove/clear slots, and set duration/start date. Adds the command IDs
to protocol.py.

Viewing (admin, OpenTTDAdminClient.get_dispatch): the GameScript API has no
dispatch support, so a new server patch (docker/patches/0002-*) adds
read-only GSOrder.GetScheduledDispatch* / IsScheduledDispatchEnabled
getters, an AdminBridge GameScript get_dispatch handler exposes them, and
get_dispatch() returns the live schedules and slots (mirrors get_timetable).

Note: set_dispatch_start_date values are normalised by the engine relative
to current game time, so they read back offset from the requested value.

Includes unit + e2e tests, a demo in main.py, and protocol/timetable docs.
The AdminBridge GameScript and the patched OpenTTD-patches clone live
outside this repo; the 0002 patch file is the durable source for the latter.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_admin.py

@@ -383,6 +383,47 @@ async def test_admin_get_station_cargo_error_response():
         await task
     assert client._gs_futures == {}
 
+@pytest.mark.asyncio
+async def test_admin_get_dispatch_request_and_response():
+    client = OpenTTDAdminClient("127.0.0.1", port=3977, admin_name="TestAdmin")
+    proto = MockProtocol()
+    client._protocol = proto
+    client._transport = MockTransport()
+
+    task = asyncio.ensure_future(client.get_dispatch(7))
+    await asyncio.sleep(0)  # let the task send the request
+
+    # First use auto-subscribes to Gamescript updates, then sends the query.
+    assert len(proto.sent) == 2
+    assert proto.sent[0][2] == PacketAdminType.AdminUpdateFrequency
+    assert decode_gamescript_payload(proto.sent[1]) == {
+        "command": "get_dispatch", "vehicle_id": 7, "request_id": 1,
+    }
+
+    response = {"command": "get_dispatch", "vehicle_id": 7, "request_id": 1,
+                "enabled": 1,
+                "schedules": [{"index": 0, "duration": 3000, "start_tick": 0, "delay": 0,
+                               "reuse_slots": 0,
+                               "slots": [{"offset": 500, "flags": 0}, {"offset": 1500, "flags": 0}]}]}
+    await client.receive_ServerGamescript(None, data=response)
+    assert await task == response
+    assert client._gs_futures == {}
+
+@pytest.mark.asyncio
+async def test_admin_get_dispatch_error_response():
+    client = OpenTTDAdminClient("127.0.0.1", port=3977, admin_name="TestAdmin")
+    client._protocol = MockProtocol()
+    client._transport = MockTransport()
+
+    task = asyncio.ensure_future(client.get_dispatch(65535))
+    await asyncio.sleep(0)
+    await client.receive_ServerGamescript(
+        None, data={"command": "get_dispatch", "vehicle_id": 65535,
+                    "request_id": 1, "error": "invalid_vehicle"})
+    with pytest.raises(ValueError, match="invalid_vehicle"):
+        await task
+    assert client._gs_futures == {}
+
 @pytest.mark.asyncio
 async def test_admin_gamescript_passthrough_unmatched():
     client = OpenTTDAdminClient("127.0.0.1", port=3977, admin_name="TestAdmin")