worker orbs: run at ~30fps when reduce-effects is on (perf)

Pairs with the previous commit (orbs now run under reduce-effects). When the user has asked
for performance (reduce-effects on) we don't need the orbs at 60fps — the slow drift and sparks
are indistinguishable at 30, and dropping every other render roughly halves the per-frame canvas
cost, keeping the "orbs under reduce-effects" experiment cheap.

The canvas still ticks at 60fps and frameCount still increments every tick, so `time` stays
real-time and the drift speed is unchanged — we just draw it half as often. Precedence: the
existing fully-asleep ~20fps throttle still wins; the 30fps cap only applies awake + reduce-effects.
Chrome users with full effects keep 60fps — no reason to dim them.

webui/static/worker-orbs.js

@@ -605,10 +605,18 @@
         if (performance.now() < _scrollPauseUntil) return;
 
         frameCount++;
-        // Fully asleep: render at ~20fps. The drift is at crawl speed so the
-        // difference is invisible, and the canvas GPU cost drops by two thirds
-        // for the hours the dashboard sits idle. Wakes re-run every frame.
-        if (sleepLevel > 0.95 && frameCount % 3 !== 0) return;
+        // Frame-skip throttles. The canvas ticks at 60fps; we drop renders to cut cost.
+        // frameCount still increments every tick, so `time` below stays real-time and the
+        // drift speed is unchanged — we just draw it less often.
+        if (sleepLevel > 0.95) {
+            // Fully asleep → ~20fps: drift is at crawl speed so it's invisible, and the
+            // GPU cost drops two-thirds for the hours the dashboard sits idle.
+            if (frameCount % 3 !== 0) return;
+        } else if (window._reduceEffectsActive) {
+            // Reduce-effects on (user asked for performance) → ~30fps: the slow drift and
+            // sparks look the same, the per-frame cost roughly halves.
+            if (frameCount % 2 !== 0) return;
+        }
         const time = frameCount / 60;
         const w = canvas.width;
         const h = canvas.height;