Add DebugNfcTagEmulator in DevPlaygound

[TimoPtr]

Summary

I wanted to debug some NFC tag issue but I don't have any writable NFC tag so I've asked Claude to do an emulator of tag. This is Claude work using the android.nfc.cardemulation.HostApduService within the DevPlaygound. I tested it on Android 9 and 17 and both managed to make proper tag read by our app.

Checklist

• New or updated tests have been added to cover the changes following the testing guidelines.
• The code follows the project's code style and best_practices.
• The changes have been thoroughly tested, and edge cases have been considered.
• Changes are backward compatible whenever feasible. Any breaking changes are documented in the changelog for users and/or in the code for developers depending on the relevance.
• I have read the Open Home Foundation AI Policy.

Select exactly one option that describes AI usage in this contribution:

• I have not used AI for this contribution.
• AI assistance was used for this contribution.
• AI fully generated the code for this contribution, but I've reviewed and understood it before submitting and will respond without AI during review.

Screenshots

Any other notes

I didn't review in details the service I assumed that since it works the tag used is valid.

[Copilot]

Pull request overview

Adds a debug-only NFC tag emulator inside the Dev Playground, allowing developers to emulate a writable NFC Forum Type 4 tag via Host Card Emulation (HCE) and inspect/modify its NDEF payload for debugging tag handling.

Changes:

• Introduces a debug HostApduService + in-memory NDEF file state to emulate a writable Type 4 tag.
• Adds a Dev Playground UI screen to control the emulated tag ID and view raw/decoded NDEF content.
• Refactors NFC tag writing helpers by extracting NFCUtil.createTagUrl/createTagMessage and adds Robolectric coverage for the emulator APDU behavior.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
app/src/testDebug/kotlin/io/homeassistant/companion/android/developer/nfc/DebugNfcTagEmulatorServiceTest.kt	Adds Robolectric tests validating APDU select/read/write flows and summary updates.
app/src/main/kotlin/io/homeassistant/companion/android/nfc/NFCUtil.kt	Extracts URL/message builders for HA NFC tags and reuses them for tag writing.
app/src/main/kotlin/io/homeassistant/companion/android/nfc/NfcSetupActivity.kt	Switches tag URL construction to NFCUtil.createTagUrl.
app/src/debug/res/xml/debug_nfc_tag_apduservice.xml	Declares the HCE AID filter for an NDEF Type 4 Tag application.
app/src/debug/res/values/strings.xml	Adds a debug label string for the emulator.
app/src/debug/kotlin/io/homeassistant/companion/android/developer/nfc/DebugNfcTagEmulatorActivity.kt	New Dev Playground screen for controlling and inspecting the emulated tag.
app/src/debug/kotlin/io/homeassistant/companion/android/developer/nfc/DebugNfcTagEmulator.kt	Implements emulator state + HostApduService APDU handling and logging.
app/src/debug/kotlin/io/homeassistant/companion/android/developer/DevPlaygroundActivity.kt	Adds entry point button to launch the emulator screen.
app/src/debug/AndroidManifest.xml	Registers the emulator activity and HCE service (disabled by default).