Add project documentation: design spec, implementation plan, and progress tracking

Initial project setup with README, CLAUDE.md (AI dev context), DESIGN.md
(full technical design covering architecture, data model, coordinate system,
rendering strategy), PROJECT_PLAN.md (phased implementation steps), and
PROGRESS.md (completion tracking).

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

CLAUDE.md

@@ -0,0 +1,82 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+eng-pad is an Android note-taking app built around notebooks with an EMR pen as the primary input method. Target devices are the Supernote Manta (Android 11) and Daylight DC-1 (Android 13). Minimum API level is Android 11 (API 30).
+
+## Build Commands
+
+```bash
+./gradlew build          # Compile everything
+./gradlew test           # Run unit tests
+./gradlew lint           # Run Android Lint
+./gradlew installDebug   # Install debug APK to connected device
+
+# Run a single test class:
+./gradlew test --tests "net.metacircular.engpad.data.StrokeBlobTest"
+```
+
+## Architecture
+
+- **Kotlin + Jetpack Compose** for UI chrome (screens, toolbar, dialogs)
+- **Custom View** (`PadCanvasView`) for the drawing canvas — Compose Canvas lacks `MotionEvent` access needed for stylus input
+- **Room** (SQLite) for persistence — notebooks, pages, strokes
+- **Single Activity** with Compose Navigation (three screens: notebook list → page list → editor)
+- **Coordinate system**: 300 DPI canonical points. Regular page = 2550×3300pt, large = 3300×5100pt. Scaled to 72 DPI (×0.24) for PDF export.
+- **Input dispatch**: `TOOL_TYPE_STYLUS` → draw/erase/select, `TOOL_TYPE_FINGER` → zoom/pan
+
+## Project Documents
+
+- **DESIGN.md** — Full technical design (architecture, data model, rendering, source tree)
+- **PROJECT_PLAN.md** — All implementation steps with checkboxes. Check off steps as completed.
+- **PROGRESS.md** — What's been done, what's in progress, decisions made. Update after every step.
+
+**Keep PROJECT_PLAN.md and PROGRESS.md in sync.** When a step is completed, check it off in PROJECT_PLAN.md and log it in PROGRESS.md. When files are added, update the source tree in both DESIGN.md and this file.
+
+## Source Tree
+
+```
+eng-pad/
+├── app/
+│   ├── build.gradle.kts                              -- Module build config
+│   └── src/
+│       ├── main/
+│       │   ├── AndroidManifest.xml
+│       │   ├── kotlin/net/metacircular/engpad/
+│       │   │   ├── EngPadApp.kt                      -- Application class
+│       │   │   ├── MainActivity.kt                   -- Single activity, Compose NavHost
+│       │   │   ├── data/
+│       │   │   │   ├── db/                           -- Room database, DAOs, converters
+│       │   │   │   ├── model/                        -- Entities: Notebook, Page, Stroke, PageSize
+│       │   │   │   └── repository/                   -- NotebookRepository, PageRepository
+│       │   │   ├── ui/
+│       │   │   │   ├── navigation/NavGraph.kt        -- Route definitions
+│       │   │   │   ├── notebooks/                    -- List screen + ViewModel
+│       │   │   │   ├── pages/                        -- Page grid screen + ViewModel
+│       │   │   │   ├── editor/                       -- PadCanvasView, EditorScreen, ViewModel
+│       │   │   │   ├── export/PdfExporter.kt         -- PDF generation + sharing
+│       │   │   │   └── theme/Theme.kt                -- Material3 theme
+│       │   │   └── undo/                             -- UndoManager, UndoableAction
+│       │   └── res/
+│       └── test/                                     -- Unit tests
+├── build.gradle.kts                                  -- Root build config
+├── settings.gradle.kts
+├── gradle.properties
+├── gradle/libs.versions.toml                         -- Version catalog
+├── CLAUDE.md                                         -- This file
+├── README.md
+├── DESIGN.md                                         -- Technical design
+├── PROJECT_PLAN.md                                   -- Implementation steps
+└── PROGRESS.md                                       -- Completion tracking
+```
+
+## Key Conventions
+
+- Stroke points are packed as little-endian float BLOBs: `[x0,y0,x1,y1,...]`
+- All coordinates are in canonical space (300 DPI). Screen transform via `Matrix`.
+- Grid spacing: 60pt (~5 squares/inch). Grid is drawn on screen, excluded from exports.
+- Pen widths: 0.38mm = 4.49pt, 0.5mm = 5.91pt (at 300 DPI).
+- Two pen sizes only, no pressure sensitivity.
+- Hardware palm rejection only (EMR digitizer).