fix(dashboard): drop stale manager destroy-hiding comment + vestigial block

Follow-up to the destroy-guard removal — the bootstrap/root container is
now destroyable end-to-end. The frontend already offered DESTR0Y/PURG3
for every container; the only manager-gating left was a stale doc-comment
('destroy/purge hidden for the manager') and a vestigial bare block
wrapping the menu appends. Drop both (no behaviour change), and update the
dashboard.md menu doc: 'disabled for the bootstrap container' -> available
for any container (hive-c0re recreates it on next startup if destroyed).

frontend/packages/dashboard/src/tabs.js

@@ -249,8 +249,8 @@ window.marked = marked;
   // ─── per-agent context menu ──────────────────────────────────────────
   // Three-dot (⋮) button on each agent card for quick single-agent
   // lifecycle actions without needing to select first. State-aware:
-  // restart/stop only shown when running, start only shown when stopped,
-  // destroy/purge hidden for the manager.
+  // restart/stop only shown when running, start only shown when
+  // stopped; rebuild + destroy/purge always shown.
   // The button is CSS-invisible until the row is hovered (or menu is
   // open) so it doesn't clutter quiet rows.
 
@@ -383,20 +383,18 @@ window.marked = marked;
         `view ${c.name} journal logs`),
     );
 
-    {
-      dropdown.append(
-        menuSep(),
-        menuItem('DESTR0Y', {
-          action: '/api/destroy/',
-          confirm: `destroy ${c.name}? container removed; state + creds kept.`,
-        }),
-        menuItem('PURG3', {
-          action: '/api/destroy/',
-          body: { purge: 'on' },
-          confirm: `PURGE ${c.name}? WIPES container, config history, claude creds, and notes. no undo.`,
-        }),
-      );
-    }
+    dropdown.append(
+      menuSep(),
+      menuItem('DESTR0Y', {
+        action: '/api/destroy/',
+        confirm: `destroy ${c.name}? container removed; state + creds kept.`,
+      }),
+      menuItem('PURG3', {
+        action: '/api/destroy/',
+        body: { purge: 'on' },
+        confirm: `PURGE ${c.name}? WIPES container, config history, claude creds, and notes. no undo.`,
+      }),
+    );
 
     if (c.deployed_sha && forgeBase) {
       const li = el('li', { role: 'presentation' });