graph: the sliders re-centered on the new defaults (release polish 6.2)

The owner speaks in display values: "labels until zoom" shows ratio/0.5,
so the old default displayed 8× — and "default one" means display 1× =
ratio 0.5, one stop tighter than the round-1 value. Both ladders are
re-centered so the new defaults sit dead-center again (stop #5):

  labelZoom: [0.125, 0.175, 0.25, 0.35, 0.45, 0.5, 0.75, 1, 1.5, 2, 3]
    — default 0.5 (displays 1×); finer steps below the default, the old
    familiar run above; old stored 4/24 snap to 3.
  blur: [10, 15, 20, 25, 30, 40, 50, 60, 80, 100, 120]
    — default 40 dead-center, min 10 per the owner's suggestion, old
    ceiling kept; old 4/5/7.5 snap to the new floor.

The dead-center ladder law is restored with no exceptions; migration
pins updated (blur 8.1 → 10, labelZoom 0.5 now a member).

1428 tests, tsc, lint, build green.

tests/graph-canvas.test.ts

@@ -210,7 +210,7 @@ describe("sanitizeRegionTuning (dev number inputs)", () => {
 		const t = sanitizeRegionTuning(undefined);
 		assert.deepEqual(t, DEFAULT_REGION_TUNING);
 		const half = sanitizeRegionTuning({ blur: 7.2 });
-		assert.equal(half.blur, 7.5); // snapped to the ladder (2026-09-17)
+		assert.equal(half.blur, 10); // snapped to the new ladder floor (owner, 2026-10-07)
 		assert.equal(half.dilation, DEFAULT_REGION_TUNING.dilation);
 	});