Canvas · Plane: an endless canvas, its grid, rulers, zoom and map

A new chapter, src/canvas. InfiniteCanvas lays artboards, shapes and
guides on an endless plane over a dot grid whose step, one, two or five
times a power of ten, keeps the dots apart as it zooms out. Rulers run
along the top and left in canvas units. A drag on empty space pans from
the press, a wheel scrolls, and Command or Control with the wheel zooms
about the pointer; the owner keeps the viewport, seeded, so its own
zoom shows at once. Layers lie over the plane in view pixels.

Shapes are rectangles, ellipses, regular polygons, lines, arrows, text,
paths and notes, each in a chart hue, painted to scale; text and notes
scale their type. Artboards carry their names above them.

ZoomControls step out and in through fixed stops, fit on request, and
hold ZoomIndicator, whose press sets 100%. MiniMap draws what lies on
the canvas and the view's box, and centers the view where it is pressed
or dragged. The viewport math, the steps and the map's fit are tested
without gpui.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

TASKS.md

@@ -114,8 +114,11 @@ Per-component lines live in `tasks/`. Tags there:
 - [x] T31a Project · Tasks — `tasks/ch31-43.md`
 - [x] T31b Project · Issues and boards
 - [x] T31c Project · Plans
-- [ ] T31d Project · Time and databases
-- [ ] T32 Canvas & Design
+- [x] T31d Project · Time and databases
+- [ ] T32a Canvas · Plane — `tasks/ch31-43.md`
+- [ ] T32b Canvas · Tools
+- [ ] T32c Canvas · Panels
+- [ ] T32d Canvas · Graphs and boards
 - [ ] T33 DB & Dev Tools
 - [ ] T34 Dashboard
 - [ ] T35 Settings
@@ -369,3 +372,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T31c | 1 | FAIL | a roadmap bar's end and the workload bar's cap went untested |
 | T31c | 2 | PASS | |
 | T31d | 1 | FAIL | a focused segment past the strip's fold stayed hidden; the tracker lost focus as Start and Stop swapped; Stop and Skip went untested; percent did not refuse content |
+| T31d | 2 | PASS | |