Add on-device Android port (lwc-core, lwc-android, Compose sample)

android/.gitignore

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+.gradle/
+build/
+*.tsbuildinfo
+local.properties
+*.log
+.kotlin/

android/README.md

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+# Login with ChatGPT — Android
+
+On-device, serverless Android port of the [Login with ChatGPT](../README.md) SDK.
+Users sign in with **their own** ChatGPT subscription via OpenAI's device-code
+OAuth flow, and the app calls Codex models billed to that user — no OpenAI API key,
+and no backend to host. Tokens live on the device in the Android Keystore.
+
+## Modules
+
+| Module | What it is |
+| --- | --- |
+| [`lwc-core`](./lwc-core) | Pure Kotlin/JVM engine — device flow, token refresh, JWT parsing, Codex streaming. No Android deps; unit-tested on the JVM. Port of the TS `-core` package. |
+| `lwc-android` | Android library — `KeystoreTokenStore` (encrypted at rest), a Custom Tab launcher, and the `LoginWithChatGPT` facade. |
+| `sample` | Minimal Compose app: sign-in screen → device code → streamed chat. |
+
+## Build & run
+
+Uses the Gradle wrapper (8.11.1) — the JDK 17 toolchain and Android SDK are picked
+up from `JAVA_HOME` / `local.properties`.
+
+On a low-RAM machine (≤8 GB), add these to your user `~/.gradle/gradle.properties`
+to keep the build inside one small JVM:
+
+```properties
+org.gradle.jvmargs=-Xmx1024m -XX:MaxMetaspaceSize=512m
+org.gradle.workers.max=1
+kotlin.compiler.execution.strategy=in-process
+```
+
+```bash
+# Run the pure-JVM unit tests (body normalization + JWT parsing)
+./gradlew :lwc-core:test
+
+# Stage-0 spike: full device login + streamed reply against a REAL ChatGPT account
+./gradlew :lwc-core:run --args="Say hello in one short sentence."
+
+# Build the sample APK
+./gradlew :sample:assembleDebug
+
+# Install + launch on a running emulator/device
+./gradlew :sample:installDebug
+adb shell am start -n com.opencoredev.loginwithchatgpt.sample/.MainActivity
+```
+
+## Using the library in your own app
+
+```kotlin
+val lwc = LoginWithChatGPT(context)                    // Keystore-backed by default
+
+// Sign in
+val device = lwc.startDeviceLogin()
+lwc.openVerification(device)                           // Custom Tab; user enters device.userCode
+while (lwc.poll(device) is DevicePollResult.Pending) delay(device.interval * 1000L)
+
+// Call a model — billed to the signed-in user's ChatGPT plan
+lwc.chat(buildJsonObject { put("model", "gpt-5.5"); put("input", "Hi") })
+    .collect { delta -> /* append streamed text */ }
+```
+
+## Security & status
+
+Tokens are encrypted at rest via Android-Keystore-backed `EncryptedSharedPreferences`
+(see [`lwc-core/README`](./lwc-core/README.md) for the trust-boundary notes). This
+rides OpenAI's unofficial Codex OAuth client, so it may break if OpenAI changes an
+endpoint — every URL/id is overridable through `ChatGPTConfig`.

android/build.gradle.kts

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+// Root build: declare plugin versions once; modules apply them without versions.
+plugins {
+    id("com.android.application") version "8.7.3" apply false
+    id("com.android.library") version "8.7.3" apply false
+    id("org.jetbrains.kotlin.android") version "2.0.21" apply false
+    id("org.jetbrains.kotlin.jvm") version "2.0.21" apply false
+    id("org.jetbrains.kotlin.plugin.compose") version "2.0.21" apply false
+    id("org.jetbrains.kotlin.plugin.serialization") version "2.0.21" apply false
+}

android/gradle.properties

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+org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
+org.gradle.caching=true
+kotlin.code.style=official
+android.useAndroidX=true

android/gradle/wrapper/gradle-wrapper.properties

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+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.11.1-bin.zip
+networkTimeout=10000
+retries=0
+retryBackOffMs=500
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists