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.

dataflow-gamepad.yml

@@ -0,0 +1,84 @@
+# The same bench, with a real gamepad and a probe.
+#
+# `dataflow.yml` is what CI validates, and it deliberately has no pad in it: the
+# pad is `dora-joy`, another repo, and pulling it in by `git:` would cost that
+# file its one property — that it resolves and runs from this checkout alone.
+# This file is the other half. It needs the network on first build, and a pad.
+#
+# The bench answers services and publishes telemetry but never moves anything.
+# What this is for is watching the node decide: the lease changing hands, the
+# deadman firing when you let go, and the arm being stopped when the pad — or
+# the node reading it — goes away.
+#
+# Run it under a coordinator rather than `dora run`, so `dora topic` can read the
+# wire and so the probe has something to attach to:
+#
+#   dora up
+#   dora start dataflow-gamepad.yml --uv --name teleop-bench
+#   dora-teleop-probe                                   # in another terminal
+#   dora topic echo -d teleop-bench teleop/jog
+#   dora stop --name teleop-bench && dora down
+
+strict_types: true
+
+debug:
+  enable_debug_inspection: true
+
+nodes:
+  - id: joy
+    git: https://gitea.liria.cl/liria/dora-joy.git
+    tag: v0.1
+    build: pip install .
+    path: dora-joy
+    inputs:
+      tick: dora/timer/millis/20
+    outputs:
+      - joy
+
+  - id: teleop
+    path: dora-teleop
+    build: pip install .
+    inputs:
+      tick: dora/timer/millis/50
+      # queue_size 1: joy ticks at 20 ms and this node at 50, so without it the
+      # loop would work through a backlog of readings that have already been
+      # overtaken. An arm should be driven by the newest one or by none.
+      joy:
+        source: joy/joy
+        queue_size: 1
+        queue_policy: drop_oldest
+      clients: bench/clients
+      response: bench/response
+      robot_state: bench/robot_state
+      tcp_pose: bench/tcp_pose
+      joint_pose: bench/joint_pose
+    outputs:
+      - twist
+      - command
+      - jog
+      - request
+      - ui_state
+    env:
+      SPEED_MM_S: "60"
+      SPEED_DEG_S: "30"
+
+  # Declared, not spawned: `dora-teleop-probe` attaches to this id when you run
+  # it, and the dataflow runs perfectly well when nobody does.
+  - id: teleop-probe
+    path: dynamic
+    inputs:
+      joy: joy/joy
+
+  - id: bench
+    path: examples/bench.py
+    inputs:
+      tick: dora/timer/millis/200
+      jog: teleop/jog
+      request: teleop/request
+      ui_state: teleop/ui_state
+    outputs:
+      - response
+      - robot_state
+      - tcp_pose
+      - joint_pose
+      - clients