Implement Phase 3: canvas drawing with stylus input

- PadCanvasView: custom View with stylus event handling (historical points
  for smoothness), Path/Paint stroke rendering, backing bitmap at 1/4
  resolution, 60pt grid drawing, Matrix coordinate transform
- CanvasState: tool modes (fine/medium pen, eraser, select), zoom/pan state
- EditorViewModel: loads/saves strokes to Room on completion
- EditorScreen: Compose wrapper with AndroidView + FilterChip toolbar
- NavGraph: pages route auto-navigates to first page editor, page size
  passed through route params

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

PROGRESS.md

@@ -41,9 +41,24 @@ See PROJECT_PLAN.md for the full step list.
 - [x] 2.5: Navigation wired — tap notebook → pages stub, editor stub
 - EngPadTheme: high-contrast light color scheme (black on white for e-ink)
 
+### Phase 3: Canvas — Basic Drawing (2026-03-24)
+
+- [x] 3.1–3.4: PadCanvasView — stylus input with historical points, Path/Paint
+  stroke rendering, backing bitmap at 1/4 resolution, 60pt grid, Matrix
+  coordinate transform (canonical ↔ screen)
+- [x] 3.5: CanvasState — tool enum (PEN_FINE, PEN_MEDIUM, ERASER, SELECT),
+  zoom/pan state, pen width constants (4.49pt, 5.91pt)
+- [x] 3.6: EditorViewModel — loads strokes from Room, saves on completion
+- [x] 3.7: EditorScreen + Toolbar — Compose wrapper with AndroidView,
+  FilterChip toolbar for pen size and eraser selection
+- [x] 3.8: NavGraph updated — pages route auto-navigates to first page's editor,
+  page size passed through route params
+- Used KTX Canvas extensions (withMatrix, withScale, createBitmap) per lint
+- ClickableViewAccessibility suppressed on PadCanvasView (drawing view)
+
 ## In Progress
 
-Phase 3: Canvas — Basic Drawing
+Phase 4: Zoom and Pan
 
 ## Decisions & Deviations