Implement Phase 1: project skeleton and data layer

Android project with Kotlin, Jetpack Compose, and Room. Includes:
- Gradle build system with version catalog, foojay JDK resolver, lint config
- Room entities (Notebook, Page, Stroke) with packed float BLOB encoding
- DAOs and repositories for all entities
- Unit tests for blob roundtrip and PageSize enum (10 tests, all passing)
- Minimal Application class and stub MainActivity

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/proguard-rules.pro

@@ -0,0 +1,3 @@
+# eng-pad ProGuard rules
+# Room
+-keep class net.metacircular.engpad.data.model.** { *; }