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>

lib/openttd/protocol.py

@@ -48,10 +48,45 @@ def read_varuint_signed(data):
     return value, rest
 
 class GameCommand(IntEnum):
+    DeleteOrder = 51
+    InsertOrder = 52
     ChangeTimetable = 174
     SetVehicleOnTime = 176
     AutofillTimetable = 177
     SetTimetableStart = 180
+    # Scheduled dispatch (JGRPP)
+    SchDispatch = 205
+    SchDispatchAdd = 206
+    SchDispatchRemove = 207
+    SchDispatchSetDuration = 208
+    SchDispatchSetStartDate = 209
+    SchDispatchClear = 213
+    SchDispatchAddNewSchedule = 214
+    SchDispatchRemoveSchedule = 215
+
+# Sentinel VehicleOrderID meaning "append to the end of the order list" for InsertOrder.
+INVALID_VEH_ORDER_ID = 0xFFFF
+
+class OrderType(IntEnum):
+    """OrderType occupies bits 0-3 of an order's `type` byte (bits 6-7 hold OrderNonStopFlags)."""
+    GotoStation = 1
+    GotoDepot = 2
+    GotoWaypoint = 6
+
+class OrderNonStopFlags(IntEnum):
+    """Packed into bits 6-7 of an order's `type` byte."""
+    StopEverywhere = 0
+    NoStopAtIntermediate = 1
+    NoStopAtDestination = 2
+    NoStopAtAny = 3
+
+class OrderStopLocation(IntEnum):
+    """Packed into bits 4-5 of an order's `type` byte. Near-end/middle/through are train-only;
+    FarEnd is the only value the server accepts for every vehicle type, so it is the safe default."""
+    PlatformNearEnd = 0
+    PlatformMiddle = 1
+    PlatformFarEnd = 2
+    PlatformThrough = 3
 
 class ModifyTimetableFlags(IntEnum):
     WaitTime = 0