fix(dashboard): wire data-async form submit handler on the C0R3 page

Clicking "update & rebuild" (and cancel / respawn / purge) on /core.html
navigated to the bare `ok` response page instead of submitting async. The
C0R3 page (split out of the dashboard) carries `data-async` forms but its
bundle never had the global submit interceptor — that handler lived inline
in tabs.js, so only the dashboard bundle had it. The forms POSTed natively
and the browser followed the response.

Fix: lift the `data-async` submit handler out of tabs.js into a shared
`bindAsyncForms(onSuccess)` in common.js (which already owns the `form`
helper that builds these forms), and call it from both pages:
- tabs.js: `bindAsyncForms(() => refreshState())` — behaviour-preserving
  (same handler, now imported).
- core.js: add a `refreshState()` (re-fetch /api/state + re-render) used
  for the cold load and as the post-submit refresh, and call
  `bindAsyncForms(() => refreshState())` at boot.

Forms with `data-no-refresh` (e.g. meta-update, which gets its update via
the meta SSE events) skip the refresh, same as before.

frontend/packages/dashboard/src/core.js

@@ -11,7 +11,7 @@
 // dashboard SYST3M tab); the dashboard keeps its own copies for now —
 // de-duplication + removing the SYST3M tab is a deliberate follow-up.
 
-import { $, el, form, openStream, initServerWarnings } from './common.js';
+import { $, el, form, openStream, initServerWarnings, bindAsyncForms } from './common.js';
 import { fmtAgo, fmtElapsed, truncate } from './util.js';
 import { createTabStrip } from '@hive/shared/tabs.js';
 
@@ -503,9 +503,28 @@ const SSE_HANDLERS = {
 };
 
 // ─── boot ─────────────────────────────────────────────────────────────────
+// Re-fetch /api/state, re-sync the derived state, re-render. Used for the
+// cold load and as the post-submit refresh for `data-async` forms whose
+// mutation doesn't arrive via an SSE event (e.g. the meta-update / spawn /
+// purge actions that opt out of `data-no-refresh`).
+async function refreshState() {
+  try {
+    const resp = await fetch('/api/state');
+    if (resp.ok) syncFromSnapshot(await resp.json());
+  } catch {
+    // best-effort: the page keeps its last-rendered state
+  }
+  renderAll();
+}
+
 async function init() {
   initServerWarnings();
 
+  // `data-async` form submit interceptor — without this the meta-update /
+  // cancel / respawn / purge buttons POST natively and the browser navigates
+  // to the bare `ok` response page.
+  bindAsyncForms(() => refreshState());
+
   // Hash-routed sub-tab strip; default Rebuild Queue. Container-load
   // polling runs only while the LOAD sub-tab is open (cpu is a short
   // two-sample read each refresh on the server).
@@ -517,15 +536,7 @@ async function init() {
     },
   });
 
-  try {
-    const resp = await fetch('/api/state');
-    if (resp.ok) {
-      syncFromSnapshot(await resp.json());
-    }
-  } catch {
-    // best-effort: the page still renders its empty states
-  }
-  renderAll();
+  await refreshState();
 
   const es = openStream('/dashboard/stream');
   if (es) {