feat(tools): persona selector across standalone tools + dashboard chat

Wire the legal-domain persona picker into corpus, deep-research, korrespond and
the dashboard chat. Each endpoint reads the chosen profile, resolves its packages
against client 57, and scopes retrieval via package_ids (falling back to family
when omitted). New dashboard tenants now subscribe to all DBN domain packages so
persona switching survives the subscription intersection.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

assets/css/tools.css

@@ -3726,6 +3726,18 @@ a.passage-card__title:hover { color: var(--ink); }
 }
 .drill-sort-select:focus { border-color: var(--teal); }
 
+.corpus-persona {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+}
+.corpus-persona__label {
+  font-size: 0.72rem;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  color: var(--muted);
+}
+
 .drill-loading,
 .drill-empty,
 .drill-error {