tabs.js: final cookie scrub — 0 issue refs (#712 batch 14)

Final pass on tabs.js. All 6 remaining cookies were either
attribution refs to closed issues / past reviews or pure-history
mile-markers:

- #259 disabled meta-update state → drop attribution
- dashboard.rs#2170 backend handler line ref → drop the line
  number (handler still lives in dashboard.rs, line drifts)
- mara on #695 M0V3 picker any-selection → drop attribution
  (substance already captured in docs/web-ui.md::Selection bar)
- #541 journald scroll surface → drop the migration history
  framing, keep present-state behaviour
- argus on #471 textContent vs innerHTML review → drop the review
  attribution, keep the safer-pattern rationale inline
- #369 tab routing section header → drop the cookie, keep the
  section divider

tabs.js: 6 → 0 issue-ref cookies (100% reduction). Across
batches 1-14 (#712): 73 → 0 issue-ref cookies, with substantive
prose (Topology tree CSS geometry, Container row icon layout,
Pending-state derivation, Selection bar, R3BU1LD QU3U3 cancel +
step annotations, Approval card requested-at, SSE multiplexing
worker-death self-heal, FL0W page MESS4GE FL0W body layout)
migrated to docs/web-ui.md across the batches.

dashboard SPA files all at 0 cookies now (PR #795 covers the
other dashboard files; this PR covers the tabs.js residual).

frontend/packages/dashboard/src/tabs.js

@@ -178,7 +178,7 @@ window.marked = marked;
   // agent rebuild ripple) runs in the background. Cold-loaded from
   // `s.meta_update_running`, then flipped live by the
   // `meta_update_running` event. Drives the META INPUTS panel's
-  // disabled "updating…" state (issue #259).
+  // disabled "updating…" state.
   let metaUpdateRunning = false;
   function syncTombstonesFromSnapshot(s) {
     tombstonesState = (s.tombstones || []).slice();
@@ -802,7 +802,7 @@ window.marked = marked;
     //                   and own descendants on the client side; the
     //                   backend rechecks via `topology::set_parent`).
     //
-    // Backend lives at POST /api/topology/set-parent (dashboard.rs#2170),
+    // Backend lives at POST /api/topology/set-parent (dashboard.rs),
     // form-encoded `child=<name>&new_parent=<target-or-empty>`. The
     // backend re-emits container snapshots on success, so the tree
     // repaints without a separate refresh.
@@ -830,11 +830,10 @@ window.marked = marked;
     });
 
     // M0V3 → <pick>: inline `<select>` of candidate parents + submit
-    // button. Available for any selection size (mara on #695 — was
+    // button. Available for any selection size. Picker omits each
-    // single-agent only in v1). Picker omits each selected agent itself
+    // selected agent itself plus the union of every selected agent's
-    // plus the union of every selected agent's descendants (cycle-safe;
+    // descendants (cycle-safe; backend `topology::set_parent`
-    // backend `topology::set_parent` re-checks). Empty candidate list ⇒
+    // re-checks). Empty candidate list ⇒ disable the picker.
-    // disable the picker.
     const candidates = validReparentCandidates(selected, containers);
     const wrap = el('span', { class: 'move-picker' });
     const selectTitle = selected.length === 1
@@ -1033,11 +1032,9 @@ window.marked = marked;
             pre.textContent = 'error: ' + resp.status + '\n' + text;
           } else {
             pre.textContent = text || '(empty)';
-            // Auto-scroll to the newest lines on fresh fetch. #541
+            // Auto-scroll to the newest lines on fresh fetch. The
-            // moved the scroll surface from side-panel-body onto the
+            // scroll surface is the <pre> itself (panel-body fills
-            // <pre> itself (the panel-body now fills the viewport and
+            // the viewport, <pre> is the inner overflow container).
-            // the <pre> is the inner overflow container), so scroll
-            // the <pre> instead of the side-panel-body.
             pre.scrollTop = pre.scrollHeight;
           }
         } catch (err) {
@@ -2946,9 +2943,9 @@ window.marked = marked;
     if (!confirm(prompt)) return;
     // Capture child nodes so we can restore on error, then replace
     // with DOM-built content (textContent + element children rather
-    // than innerHTML — per argus's review note on #471, the format
+    // than innerHTML — the format string only carries server-side
-    // string only carries server-side ints/bool today but textContent
+    // ints/bool today but textContent is the safer pattern if a
-    // is the safer pattern if a stringy field ever lands).
+    // stringy field ever lands).
     const originalChildren = btn ? Array.from(btn.childNodes) : [];
     const restoreBtn = () => {
       if (!btn) return;
@@ -3206,7 +3203,7 @@ window.marked = marked;
     };
   })();
 
-  // ─── tab routing (#369) ────────────────────────────────────────────────
+  // ─── tab routing ───────────────────────────────────────────────────────
   // Hash-based: `#swarm` / `#call` / `#system` activate the matching
   // pane on the dashboard. Empty hash defaults to SW4RM. FL0W is NOT
   // a tab — it's a separate page (`/flow.html`) reached via the