Let graphs zoom out to an eighth (#387)

With the Chip and the Filter drawn as devices, a preset such as the
Laser is about 3060 units wide. In a window of 1280 px a fit then hit
the floor of 0.25 and cut the Notes node off on the left.

- ZOOM_LIMITS.min goes from 0.25 to 0.125. The graph zooms without
  steps, so one more step is the floor halved. 0.125 is also the
  smallest step of the scene view.
- It holds for the wheel, for Fit and for the node board of plugins.
- The grid still hides itself below 8 px, so it does not flicker.

Tests:
- Unit plugins and graph-framing: 55 tests green, the floor test now
  expects 0.125.
- e2e 06 (atx): ALL PASSED, 149 checks. Only a comment that named 0.25
  changed there.
- Gate (atx): CHECK EXIT 0, 285 files, 4377 tests.

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

tests/editor/plugins.test.ts

@@ -613,6 +613,6 @@ describe('zooming a graph view about a point', () => {
 
   it('stops at the zoom limits', () => {
     expect(zoomedAbout({ pan: { x: 0, y: 0 }, zoom: 2 }, { x: 0, y: 0 }, 10).zoom).toBe(2.5);
-    expect(zoomedAbout({ pan: { x: 0, y: 0 }, zoom: 0.3 }, { x: 0, y: 0 }, 0.1).zoom).toBe(0.25);
+    expect(zoomedAbout({ pan: { x: 0, y: 0 }, zoom: 0.3 }, { x: 0, y: 0 }, 0.1).zoom).toBe(0.125);
   });
 });