Abandon velocity-weighted region opacity (owner-rejected, buggy at scale)

Per-node speed is invisible inside a cluster blob (still neighbors'
skeleton strokes dominate the local area), and per-cluster max-speed
couples everything: dragging ONE node dimmed the whole cluster's blob
to nothing — including disconnected members at near-zero velocity.
Neither granularity is right, so the idea is withdrawn entirely.

Manual revert of the velocity parts (a git revert of 154f6c8 would
have resurrected the frame fade): weight ramp, position stamps, EMA
state, motion-pending flush, per-edge stroke batching, and the tests.
Region splat is back to full-opacity coverage at rest AND in motion
(2026-09-14 no-stacking invariant). The regions.enabled compute off
switch stays.

tests/graph-canvas.test.ts

@@ -17,7 +17,6 @@ import {
 	fitTransform,
 	labelAlpha,
 	pickNearest,
-	regionVelocityWeight,
 	zoomRatioOf,
 	LABELS_FADE_SPAN,
 } from "../components/graph-canvas.ts";
@@ -228,28 +227,3 @@ describe("sanitizePhysicsTuning (physics controls)", () => {
 	});
 });
 
-describe("regionVelocityWeight", () => {
-	test("still nodes: at or below the still threshold → full opacity", () => {
-		assert.equal(regionVelocityWeight(0), 1);
-		assert.equal(regionVelocityWeight(1.5), 1);
-	});
-
-	test("fast nodes: at or above the moving threshold → blob off", () => {
-		assert.equal(regionVelocityWeight(8), 0);
-		assert.equal(regionVelocityWeight(100), 0);
-	});
-
-	test("linear ramp between the thresholds, monotone decreasing", () => {
-		const mid = regionVelocityWeight((1.5 + 8) / 2);
-		assert.ok(Math.abs(mid - 0.5) < 1e-12);
-		// strictly decreasing across the ramp
-		for (let s = 1.5; s <= 8; s += 0.25) {
-			assert.ok(regionVelocityWeight(s) >= regionVelocityWeight(s + 0.25));
-		}
-		// never leaves [0, 1]
-		for (let s = -10; s <= 50; s += 1.7) {
-			const w = regionVelocityWeight(s);
-			assert.ok(w >= 0 && w <= 1);
-		}
-	});
-});