Update docs for DC-1 testing, fix toolbar clipping

- Updated DESIGN.md: rendering strategy (no backing bitmap, screen-space
  grid, viewport clamping), added line snap and box tool documentation
- Updated PROGRESS.md: DC-1 testing results and fixes applied
- Updated CLAUDE.md: key conventions for rendering
- Fix toolbar overlap: use clipToBounds on canvas AndroidView to prevent
  it from drawing over the toolbar area

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

PROGRESS.md

@@ -44,9 +44,10 @@ See PROJECT_PLAN.md for the full step list.
 ### 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),
+  stroke rendering, direct path drawing (no backing bitmap), 60pt grid
+  drawn in screen space with pixel-snapped positions, Matrix coordinate
+  transform (canonical ↔ screen)
+- [x] 3.5: CanvasState — tool enum (PEN_FINE, PEN_MEDIUM, ERASER, SELECT, BOX),
   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,
@@ -58,18 +59,19 @@ See PROJECT_PLAN.md for the full step list.
 
 ### Phase 4: Zoom and Pan (2026-03-24)
 
-- [x] 4.1: ScaleGestureDetector with focal-point zoom (0.5×–4×)
-- [x] 4.2: Finger drag for pan with multi-pointer tracking (handles finger
-  swaps during pinch gestures)
+- [x] 4.1: ScaleGestureDetector with focal-point zoom (dynamic min–4×)
+- [x] 4.2: Finger drag for pan with multi-pointer tracking, pan clamped
+  so page always fills viewport
 - [x] 4.3: Input routing by tool type already in place from Phase 3
 - Zoom/pan state managed locally in PadCanvasView for responsiveness,
   synced to ViewModel on gesture end
+- Minimum zoom computed dynamically from page/view dimensions
 
 ### Phase 5: Eraser (2026-03-24)
 
 - [x] 5.1–5.3: Stroke-level eraser with bounding box hit test (42pt radius),
   processes historical touch points for thorough erasing, deletes from
-  view + Room DB, rebuilds backing bitmap
+  view + Room DB
 
 ### Phase 6: Undo/Redo (2026-03-24)
 
@@ -110,12 +112,29 @@ See PROJECT_PLAN.md for the full step list.
 - [x] 10.3: Empty states and delete confirmations already in place from Phase 2
 - [ ] 10.4: Performance profiling — requires on-device testing
 
+### On-Device Testing — Daylight DC-1 (2026-03-24)
+
+Tested on DC-1, identified and fixed rendering issues:
+
+- **Grid**: original grid drawn in canonical space had uneven spacing due to
+  sub-pixel positioning when scaled. Fixed by drawing grid in screen space
+  with pixel-snapped line positions. Now uniform squares.
+- **Stroke quality**: original backing bitmap at 1/4 resolution caused blurry
+  strokes. Fixed by removing backing bitmap entirely and drawing paths directly.
+  Anti-aliasing disabled on all paint for crisp e-ink lines.
+- **Viewport**: dark gray background was visible around page edges. Fixed by
+  clamping pan to page edges, computing dynamic min zoom, and white background.
+- **Box tool**: works correctly on device.
+- **PDF export**: correctly elides grid — confirmed on device.
+- **Line snap**: increased threshold to 60pt (~5mm) and switched to max-distance
+  tracking to handle EMR stylus hand tremor.
+
 ## Status
 
 All implementation phases complete. Remaining work:
-- On-device testing on Supernote Manta and Daylight DC-1
-- Performance profiling (stroke rendering, page load times)
-- Manual verification of PDF export fidelity
+- Test on Supernote Manta
+- Verify line snap behavior on device
+- Performance profiling with heavily annotated pages
 
 ## Decisions & Deviations