docs: add Examples section with 12 spoiler examples + E2E tests

README.md gets a new Examples section with collapsible <details> blocks:

NDK-native (complete runnable programs):
- Record from microphone (AAudio)
- Take a picture from camera (Camera2 + ImageReader)
- List available sensors
- Check thermal status
- Query GPU capabilities (EGL + GLES2)
- Probe available media codecs
- Read device configuration
- Decode an image file

Cross-project sketches (noting which library to use):
- Get GPS coordinates (jni/location)
- Connect to WiFi AP (jni/net/wifi)
- Send a notification (jni/app/notification)
- Query battery status (aidl)

E2E tests (tests/e2e/examples_test.go) verify the NDK examples
compile and run correctly on an Android emulator. Run with:
  make e2e-examples-test

Author: xaionaro@dx.center

Makefile

@@ -17,7 +17,7 @@ FIXTURE_MODULES := $(notdir $(wildcard tools/pkg/specgen/testdata/*/))
 NDK_SYSROOT := $(NDK_PATH)/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include
 C2FFI_BIN   ?= c2ffi
 
-.PHONY: all capi specs idiomatic clean regen fixtures test lint check-examples e2e e2e-build e2e-examples e2e-audio ndkcli ndkcli-commands
+.PHONY: all capi specs idiomatic clean regen fixtures test lint check-examples e2e e2e-build e2e-examples e2e-examples-test e2e-audio ndkcli ndkcli-commands
 
 all: specs capi idiomatic
 
@@ -108,6 +108,10 @@ e2e: e2e-build
 e2e-examples:
 	./tests/e2e/run-examples.sh
 
+# Run examples E2E Go test on Android emulator (requires running emulator + NDK)
+e2e-examples-test:
+	./tests/e2e/run-examples-test.sh
+
 # Run audio recording E2E test (requires running emulator with audio + NDK)
 e2e-audio:
 	./tests/e2e/run-audio-e2e.sh