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>

tools/e2e/06-graph.mjs

@@ -569,7 +569,7 @@ export async function graph(t) {
 
   // 6o. Fit really fits: proven against a node parked far outside, and against the fact that the
   //      graph is then wider than the canvas – otherwise centring alone would pass this check.
-  // The distance follows the canvas: a fixed 2500 units needs a zoom below the 0.25 floor once
+  // The distance follows the canvas: a fixed 2500 units can need a zoom below the floor once
   // the canvas is short, and then Fit cannot fit anything however correct it is.
   const park = Math.round(area.w);
   await evaluate(