read the gamepad from dora-joy and publish twist and command

The pad moves to dora-joy, so this node keeps no hardware dependency and the
pad becomes reusable. It arrives on `joy` as a plain reading; `JoyInput.read`
treats silence past JOY_TTL_S as absence, because that node dying looks like
silence rather than like an unplugged pad and the arm cannot tell them apart.

Both control sources are now normalised to a [-1, 1] six-vector before anything
is scaled, and the scaling happens in one function. The web path used to pass a
velocity straight through without going near mapping, which is why the console
had to speak the arm's units. It no longer does.

`twist` (SI) and `command` (robot-agnostic verbs) are the standard ports. `jog`
and `request` still carry the same intent in dora-ulite6's units and service
names so the two repositories can move independently; LEGACY_REQUEST is the
only place that knows what that node calls a verb. Wire one or the other, never
both. `joint_jog` is specified in the manifest and deliberately not built.

Schemas are declared rather than inferred: pyarrow reads a null `value` as its
own type, so an inferred `command` would change its port's type between one
verb and the next.

Three bugs found while moving this code, each with a test:

- `Sample.active` compared raw axes against a threshold, but SDL rests a
  trigger at -1.0, so every connected pad read as in use for ever: the pad took
  the lease on plug-in and GAMEPAD_IDLE_RELEASE_S never fired.
- The e-stop latch was never consulted when deciding a velocity, so Back
  stopped the arm for one tick and the next stick nudge drove it again. Nothing
  on the pad could clear it either. It is now checked above the lease, and X
  releases it and clears the controller's error, as the console's RESET does.
- Buttons were read before the arbiter granted the lease, so the first press
  after the pad had been idle was swallowed: not owned yet when read, and no
  longer a rising edge by the next tick.

tests/test_ui.py

@@ -7,18 +7,18 @@ from dora_teleop.arbiter import GAMEPAD, WEB
 
 
 def test_a_jog_carries_its_six_numbers():
-    command = ui.command_of({"type": "jog", "velocity": [1, 2, 3, 4, 5, 6]})
+    command = ui.command_of({"type": "jog", "axes": [0.1, 0.2, 0.3, 0.4, 0.5, 0.6]})
 
     assert command.type == "jog"
-    assert command.velocity == [1.0, 2.0, 3.0, 4.0, 5.0, 6.0]
+    assert command.axes == [0.1, 0.2, 0.3, 0.4, 0.5, 0.6]
 
 
 def test_a_jog_of_the_wrong_length_is_not_a_jog():
-    assert ui.command_of({"type": "jog", "velocity": [1, 2, 3]}) is None
+    assert ui.command_of({"type": "jog", "axes": [1, 2, 3]}) is None
 
 
 def test_a_jog_carrying_something_that_is_not_a_number_is_not_a_jog():
-    assert ui.command_of({"type": "jog", "velocity": [1, 2, 3, 4, 5, "fast"]}) is None
+    assert ui.command_of({"type": "jog", "axes": [1, 2, 3, 4, 5, "fast"]}) is None
 
 
 def test_a_message_we_have_never_heard_of_is_dropped_not_refused():
@@ -36,8 +36,8 @@ def test_taking_control_carries_whether_it_may_preempt():
 
 
 def test_the_gripper_button_says_which_way():
-    assert ui.command_of({"type": "gripper", "vacuum": True}).enabled is True
-    assert ui.command_of({"type": "gripper", "vacuum": False}).enabled is False
+    assert ui.command_of({"type": "gripper", "closed": True}).enabled is True
+    assert ui.command_of({"type": "gripper", "closed": False}).enabled is False
 
 
 def test_a_move_needs_a_position():
@@ -109,7 +109,8 @@ def test_the_snapshot_carries_every_key_the_page_reads_by_name():
         "arm_state",
         "owner",
         "estop",
-        "vacuum",
+        "gripper",
+        "units",
         "freedrive",
         "position",
         "joints",