Add CLAUDE.md with build commands and architecture overview

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+```bash
+./gradlew build                        # Full build with tests
+./gradlew test                         # Unit tests (Robolectric, no device needed)
+./gradlew test --tests "*ClassName*"   # Run a single test class
+./gradlew check                        # All checks including detekt lint
+./gradlew detekt                       # Code quality analysis only
+./gradlew publishToMavenLocal          # Publish to local Maven for integration testing
+./gradlew dokkaHtmlMultiModule         # Generate API documentation
+scripts/start-local-development.sh     # Continuous build + local Maven publish
+```
+
+## Architecture
+
+This is an Android SDK library (`browser-switch`) with a companion demo app (`demo`). It enables apps to open URLs in Chrome Custom Tabs or Auth Tabs and receive deep-link callback results.
+
+**Modules**: `:browser-switch` (library, published to Maven Central), `:demo` (Jetpack Compose demo app)
+
+### Core Flow
+
+1. App calls `BrowserSwitchClient.start()` with a URL and return URL scheme → library validates device capability, launches browser
+2. Browser redirects back to app's custom scheme → Android fires deep-link intent
+3. App calls `BrowserSwitchClient.completeRequest()` with stored pending request + intent → returns sealed result
+
+State persistence is the **app's responsibility**: `BrowserSwitchStartResult.Started` carries a Base64-encoded JSON string the app must store and restore across process death.
+
+### Key Classes
+
+- **`BrowserSwitchClient`** — Public API. Three constructors: no-arg (Custom Tabs only), `ActivityResultCaller` (Auth Tab for Activities), `ActivityResultRegistry` (Auth Tab for Compose). Methods: `start()` → `BrowserSwitchStartResult`, `completeRequest()` → `BrowserSwitchFinalResult`, `restorePendingRequest()`.
+- **`BrowserSwitchOptions`** — Builder for URL, request code, metadata, return URL scheme, app link URI, and `LaunchType`.
+- **`BrowserSwitchStartResult`** — Sealed Kotlin class: `Started(pendingRequest: String)` | `Failure(error: Exception)`
+- **`BrowserSwitchFinalResult`** — Sealed Kotlin class: `Success` | `Failure` | `NoResult`
+- **`AuthTabInternalClient`** — Internal. Selects Auth Tab (Chrome 137+) or falls back to Custom Tabs; requires `ActivityResultLauncher` set up in constructor.
+- **`BrowserSwitchInspector`** — Internal. Validates device can handle deep links before launch.
+- **`BrowserSwitchRequest`** — Internal. Serializes/deserializes request state to Base64-encoded JSON.
+- **`LaunchType`** — Enum: `ACTIVITY_NEW_TASK` | `ACTIVITY_CLEAR_TOP`
+
+### Testing
+
+Tests use **Robolectric** (no emulator required), JUnit 4, Mockito, and MockK. All tests live in `browser-switch/src/test/java/`. `BrowserSwitchClientUnitTest.java` is the primary test file covering the main client behavior.
+
+### Publishing
+
+Published to Maven Central via Sonatype OSSRH. Requires env vars `SONATYPE_NEXUS_USERNAME`, `SONATYPE_NEXUS_PASSWORD`, and signing keys (`SIGNING_KEY_ID`, `SIGNING_KEY_PASSWORD`, `SIGNING_KEY_FILE`). Release tasks: `changeGradleReleaseVersion`, `updateCHANGELOGVersion`, `incrementSNAPSHOTVersion`.
+
+### Versions
+
+- Current major version: v3.x; v2.x deprecated March 2026
+- compileSdk 36, minSdk 23, Java 11, Kotlin 1.9.20