feat(gamepad): controller discovery + client-negotiated pad type + rich DualSense end to end

The Apple client grows full gamepad support and punktfunk/1 learns to negotiate
the virtual pad type:

- Protocol: Hello carries a GamepadPref byte (offset 21, the same trailing-byte
  back-compat pattern as the compositor; echoed resolved in Welcome at 54).
  Host precedence: explicit client choice > PUNKTFUNK_GAMEPAD env > Xbox 360,
  DualSense (UHID) only where available. ABI: punktfunk_connect_ex2 +
  punktfunk_connection_gamepad (connect_ex delegates; ABI_VERSION stays 2 — the
  trailing byte IS the compat mechanism). punktfunk-client-rs gets --gamepad.

- Swift client: GamepadManager (app-lifetime discovery + selection — Settings
  lists every controller with capabilities/battery/"In use"; exactly ONE pad
  forwards as pad 0, auto = most recently connected, or pinned), GamepadCapture
  (snapshot-diff button/axis events, DualSense touchpad + ~250 Hz motion on the
  rich-input plane, held state released on switch/deactivate/stop),
  GamepadFeedback (rumble → CoreHaptics per-handle engines; lightbar →
  GCDeviceLight; player LEDs → playerIndex; adaptive-trigger blocks → the
  table-driven DualSenseTriggerEffect parser → GCDualSenseAdaptiveTrigger,
  exact for the 10-zone positional modes). The pad type auto-resolves from the
  physical controller at connect time, user-overridable in Settings.

- Host DualSense fixes surfaced by adversarial review against hid-playstation /
  SDL / Nielk1 ground truth: input-report sensor/touch offsets were off by one
  (the kernel read garbage motion + phantom touches), the L2/R2 trigger blocks
  were swapped (the report is right-trigger-first), feedback now gates on the
  report's valid-flags (a plain rumble write no longer blanks lightbar/
  triggers), and the touchpad rescale clamps to the advertised ABS_MT extents.

- Tests: Hello/Welcome trailing-byte back-compat, pick_gamepad precedence,
  byte-exact input-report layout, valid-flag gating, per-mode trigger-parser
  table (incl. packed 3-bit zones), wire conversions, and a scripted loopback
  feedback burst (PUNKTFUNK_TEST_FEEDBACK=1) asserted through the xcframework
  on the rumble + HID-output planes.

Validated: cargo test/clippy/fmt green on macOS + Linux (61 host tests), swift
build/test green, test-loopback.sh green, tvOS/iOS targets compile. DualSense
motion sign/scale is derived from the calibration blob, not yet live-verified
(constants isolated in GamepadWire).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/apple/test-loopback.sh

@@ -19,7 +19,9 @@ CFG="$(mktemp -d "${TMPDIR:-/tmp}/punktfunk-loopback.XXXXXX")"
 PAIR_LOG="$CFG/pairing-host.log"
 mkdir -p "$CFG/open" "$CFG/paired"
 trap 'kill "${HOST_PID:-}" "${PAIR_PID:-}" 2>/dev/null || true' EXIT
-HOME="$CFG/open" XDG_CONFIG_HOME="$CFG/open/.config" \
+# The open host also scripts a feedback burst (rumble + DualSense hidout) right after the
+# handshake, so the Swift test can assert the host→client feedback planes end to end.
+HOME="$CFG/open" XDG_CONFIG_HOME="$CFG/open/.config" PUNKTFUNK_TEST_FEEDBACK=1 \
     target/release/punktfunk-host m3-host --port "$PORT" --source synthetic --frames 300 &
 HOST_PID=$!
 HOME="$CFG/paired" XDG_CONFIG_HOME="$CFG/paired/.config" \
@@ -41,4 +43,5 @@ fi
 
 cd clients/apple
 PUNKTFUNK_LOOPBACK_PORT="$PORT" PUNKTFUNK_PAIRING_PORT="$PAIR_PORT" PUNKTFUNK_PAIRING_PIN="$PIN" \
+    PUNKTFUNK_TEST_FEEDBACK=1 \
     swift test --filter LoopbackIntegrationTests