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/conftest.py

@@ -2,10 +2,22 @@
 
 import json
 
+import pyarrow as pa
 import pytest
 
 from dora_teleop.config import Config
-from dora_teleop.gamepad import Sample
+from dora_teleop.joy import Sample
+
+# The shape `dora-joy` publishes. Declared here rather than inferred for the same
+# reason it is declared there: pyarrow reads an empty `axes` list as `list<null>`,
+# so a test for an absent pad would otherwise build a message no consumer sees.
+JOY = pa.struct(
+    [
+        ("axes", pa.list_(pa.float32())),
+        ("buttons", pa.list_(pa.bool_())),
+        ("present", pa.bool_()),
+    ]
+)
 
 
 class RecordingNode:
@@ -26,9 +38,17 @@ class RecordingNode:
         return [(data[0].as_py(), metadata) for name, data, metadata in self.sent if name == output_id]
 
     def jogs(self):
-        """Return every velocity sent to the arm, in order."""
+        """Return every velocity sent on the deprecated `jog` port, in order."""
         return [row["velocity"] for row, _ in self.outputs("jog")]
 
+    def twists(self):
+        """Return every Twist sent on the standard port, in order."""
+        return [row for row, _ in self.outputs("twist")]
+
+    def actions(self):
+        """Return the verb of every standard `command`, in order."""
+        return [row["action"] for row, _ in self.outputs("command")]
+
     def services(self):
         """Return the name of every service called, in order."""
         return [row["service"] for row, _ in self.outputs("request")]
@@ -41,20 +61,6 @@ class RecordingNode:
         self.sent.clear()
 
 
-class FakeGamepad:
-    """Stands in for the reader thread: hands back whatever the test set."""
-
-    def __init__(self, sample=None):
-        self.sample = sample or Sample()
-        self.stopped = False
-
-    def read(self):
-        return self.sample
-
-    def shutdown(self):
-        self.stopped = True
-
-
 def stick(axes=None, buttons=None, present=True):
     """Build one gamepad reading, padded to a full six axes."""
     values = list(axes or [])
@@ -67,6 +73,20 @@ def stick(axes=None, buttons=None, present=True):
     return Sample(axes=values, buttons=list(buttons or []), present=present)
 
 
+def joy_message(sample):
+    """Build the Arrow row `dora-joy` would publish for one reading."""
+    return pa.array(
+        [
+            {
+                "axes": [float(value) for value in sample.axes],
+                "buttons": [bool(down) for down in sample.buttons],
+                "present": sample.present,
+            }
+        ],
+        type=JOY,
+    )
+
+
 def input_event(event_id, value, metadata=None):
     """Build the event dict dora hands a node for one input."""
     return {"type": "INPUT", "id": event_id, "value": value, "metadata": dict(metadata or {})}
@@ -80,8 +100,8 @@ def clean_env(monkeypatch):
         "SPEED_DEG_S",
         "DEADZONE",
         "EXPO",
-        "JOYSTICK_INDEX",
         "JOG_TTL_S",
+        "JOY_TTL_S",
         "GAMEPAD_IDLE_RELEASE_S",
         "STATE_POLL_S",
     ):