Rebuild: edge:node --max-mbit caps a node's download

For workers on a shared line (poweredge-kantoor: 160 Mbit/s): the range
stream is read at most at the cap, TCP holds the coordinator back. The
cap is the node's, split over its processes (also EDGE_MAX_MBIT).
REBUILD.md: where workers run (connections set the speed; remote workers
take CPU off homelab).

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

tests/unit/edge/throttle.spec.ts

@@ -0,0 +1,16 @@
+import { test } from '@japa/runner'
+import { throttle } from '#lib/edge/index'
+
+test.group('edge / throttle', () => {
+  test('passes everything on, at most the given rate after the first second', async ({ assert }) => {
+    const pieces = Array.from({ length: 30 }, (_, i) => new Uint8Array(1000).fill(i))
+    const started = Date.now()
+    const out: Uint8Array[] = []
+    // 30,000 bytes at 20,000 B/s: the first 20,000 at once, the rest over ~0.5 s.
+    for await (const piece of throttle(pieces, 20_000)) out.push(piece)
+    const seconds = (Date.now() - started) / 1000
+    assert.deepEqual(out, pieces)
+    assert.isAtLeast(seconds, 0.45)
+    assert.isBelow(seconds, 1.2)
+  })
+})