feat: replace gomobile examples with real gomobile bind AAR build

Replace fake println-based examples with a real gomobile-bindable
package that produces an AAR via `gomobile bind`. The sensorbridge
package:

- Wraps sensor.Manager with int64 handle transport (gomobile bind
  cannot export unsafe.Pointer or uintptr)
- Builds to sensorbridge.aar with generated Java classes:
  Bridge(long managerHandle), accelerometerName(), handle(), etc.
- Includes Makefile for `make` to build the AAR
- Uses separate go.mod to avoid polluting the main module

Verified: `gomobile bind` produces 1.5MB AAR with correct Java API
(sensorbridge/Bridge.class, sensorbridge/Sensorbridge.class).

Author: xaionaro@dx.center

examples/gomobile/sensor-bridge/main.go

@@ -0,0 +1,2 @@
+*.aar
+*-sources.jar

examples/gomobile/sensorbridge/.gitignore

@@ -0,0 +1,23 @@
+ANDROID_HOME ?= $(HOME)/Android/Sdk
+GOMOBILE     ?= $(shell go env GOPATH)/bin/gomobile
+API_LEVEL    ?= 35
+
+AAR := sensorbridge.aar
+
+.PHONY: all clean install-tools
+
+all: $(AAR)
+
+$(AAR): sensorbridge.go
+	ANDROID_HOME=$(ANDROID_HOME) $(GOMOBILE) bind \
+		-target=android/arm64 \
+		-androidapi=$(API_LEVEL) \
+		-o $@ .
+
+install-tools:
+	go install golang.org/x/mobile/cmd/gomobile@latest
+	go install golang.org/x/mobile/cmd/gobind@latest
+	$(GOMOBILE) init
+
+clean:
+	rm -f $(AAR) sensorbridge-sources.jar

examples/gomobile/sensorbridge/Makefile

@@ -0,0 +1,10 @@
+module github.com/AndroidGoLab/ndk/examples/gomobile/sensorbridge
+
+go 1.25.0
+
+require (
+	github.com/AndroidGoLab/ndk v0.0.3
+	golang.org/x/mobile v0.0.0-20260312152759-81488f6aeb60
+)
+
+replace github.com/AndroidGoLab/ndk => ../../..

examples/gomobile/sensorbridge/go.mod

@@ -0,0 +1,2 @@
+golang.org/x/mobile v0.0.0-20260312152759-81488f6aeb60 h1:MOzyaj0wu2xneBkzkg9LHNYjDBB4W5vP043A2SYQRPA=
+golang.org/x/mobile v0.0.0-20260312152759-81488f6aeb60/go.mod h1:th6VJvzjMbrYF8SduQY5rpD0HG0GleGxjadkqSxFs3k=

examples/gomobile/sensorbridge/go.sum

@@ -0,0 +1,82 @@
+// Package sensorbridge exposes NDK sensor access to Java/Kotlin
+// via gomobile bind.
+//
+// Build with:
+//
+//	gomobile bind -target=android -androidapi=26 ./examples/gomobile/sensorbridge
+//
+// This produces sensorbridge.aar + sensorbridge-sources.jar.
+//
+// Java usage:
+//
+//	import sensorbridge.Sensorbridge;
+//	import sensorbridge.Bridge;
+//
+//	long ptr = nativeGetSensorManager(); // from JNI
+//	Bridge bridge = Sensorbridge.newBridge(ptr);
+//	String name = bridge.accelerometerName();
+//	bridge.close();
+package sensorbridge
+
+import (
+	"github.com/AndroidGoLab/ndk/sensor"
+)
+
+// Bridge wraps an ASensorManager for cross-language use.
+// Unexported fields are invisible to Java/Kotlin.
+type Bridge struct {
+	mgr *sensor.Manager
+}
+
+// NewBridge creates a Bridge from a raw ASensorManager* passed as int64
+// (Java long). gomobile bind does not support unsafe.Pointer or uintptr,
+// so native handles must be transported as int64.
+func NewBridge(managerHandle int64) *Bridge {
+	return &Bridge{
+		mgr: sensor.NewManagerFromUintPtr(uintptr(managerHandle)),
+	}
+}
+
+// Handle returns the underlying ASensorManager* as int64 for passing
+// back to Java/JNI code.
+func (b *Bridge) Handle() int64 {
+	return int64(b.mgr.UintPtr())
+}
+
+// AccelerometerName returns the name of the default accelerometer,
+// or empty string if unavailable.
+func (b *Bridge) AccelerometerName() string {
+	return b.sensorName(sensor.Accelerometer)
+}
+
+// GyroscopeName returns the name of the default gyroscope,
+// or empty string if unavailable.
+func (b *Bridge) GyroscopeName() string {
+	return b.sensorName(sensor.Gyroscope)
+}
+
+// LightSensorName returns the name of the default light sensor,
+// or empty string if unavailable.
+func (b *Bridge) LightSensorName() string {
+	return b.sensorName(sensor.Light)
+}
+
+// SensorName returns the name of a sensor by its Android type code,
+// or empty string if the sensor is not available.
+func (b *Bridge) SensorName(sensorType int32) string {
+	return b.sensorName(sensor.Type(sensorType))
+}
+
+func (b *Bridge) sensorName(t sensor.Type) string {
+	s := b.mgr.DefaultSensor(t)
+	if s.UintPtr() == 0 {
+		return ""
+	}
+	return s.Name()
+}
+
+// Close is a no-op — the ASensorManager is a singleton owned by the
+// system. Provided so the Bridge satisfies Java's Closeable pattern.
+func (b *Bridge) Close() {
+	b.mgr = nil
+}