release(v1.7.26-alpha): mirror list + origin-relative download URLs

Adds a multi-mirror manifest fetch. `check_for_updates` walks a
configurable list (data_dir/update-mirrors.json) in priority order
and falls through to the next mirror on any HTTP / parse / timeout
failure. Two defaults bake in: Server 1 (git.tx1138.com) and Server 2
(23.182.128.160:3000).

Critical fix: after parsing a manifest, rewrite every component's
`download_url` so its origin matches the manifest URL we fetched.
Before this, the manifest hard-coded absolute URLs pointing at one
specific server — so even when a node fetched the manifest from a
faster mirror, the actual 200MB download went back to the slow
original. Now the faster mirror wins end-to-end.

New RPCs: update.list-mirrors, update.add-mirror, update.remove-mirror,
update.set-primary-mirror. New UI section on the System Update page
for operator management. 5 new unit tests for origin parsing and
manifest rewriting (21/21 green).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

neode-ui/src/views/settings/AccountInfoSection.vue

@@ -180,6 +180,19 @@ init()
               </button>
             </div>
             <div class="overflow-y-auto flex-1 min-h-0 space-y-6 pr-1">
+              <!-- v1.7.26-alpha -->
+              <div>
+                <div class="flex items-center gap-2 mb-3">
+                  <span class="text-xs font-mono px-2 py-0.5 rounded bg-orange-500/20 text-orange-300">v1.7.26-alpha</span>
+                  <span class="text-xs text-white/40">Apr 21, 2026</span>
+                </div>
+                <div class="space-y-3 text-sm text-white/80 pl-3 border-l border-white/10">
+                  <p>Update downloads now have a mirror list. If the primary update server is slow or unreachable, your node automatically tries the next mirror and downloads the files from there — no more waiting on a stalled server with no recourse.</p>
+                  <p>A new 'Update mirrors' section on the System Update page lets you see the list, add your own mirror URL, reorder which is tried first (Set primary), or remove one. The primary is tagged with a green PRIMARY pill.</p>
+                  <p>Downloads automatically follow the mirror that served the manifest. Previously every mirror served the same manifest, and the manifest's download URLs were hardcoded to a single server — so even picking a faster mirror couldn't speed up the actual download. Now the backend rewrites download URLs to match whichever mirror succeeded.</p>
+                  <p>Ships with two defaults: Server 1 (tx1138) and Server 2 (VPS). Add the URL format <code>https://host/.../releases/manifest.json</code> for custom mirrors.</p>
+                </div>
+              </div>
               <!-- v1.7.25-alpha -->
               <div>
                 <div class="flex items-center gap-2 mb-3">