fix(ux): T4 polish wave — empty-contact filter, redirect-on-create, friendly stage errors

F19: client form drops empty-value contacts on submit; auto-promotes first remaining row to primary if none flagged.
F20: new-interest dialog redirects to the detail page on create instead of bouncing back to the list.
F21: stage-transition validation errors render with STAGE_LABELS — "Yacht is required before leaving the Enquiry stage." (was "yachtId is required before leaving stage=enquiry").
F22: blocked-stage marker swapped from the ⚑ unicode glyph to a Lucide AlertTriangle with aria-label.
F25: documents-hub folder selection moves to ?folder=<id> querystring so deep-link / browser-back / refresh round-trip the current folder.
F26: reopen-outcome action now toasts "Outcome cleared — interest is open again."
F27: stage PATCH where target === current short-circuits to a no-op return; downstream callers don't see a phantom stage_change audit row.

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

src/components/clients/client-form.tsx

@@ -176,9 +176,30 @@ export function ClientForm({
 
   const mutation = useMutation({
     mutationFn: async (data: CreateClientInput) => {
+      // F19: drop contact rows whose value is empty/whitespace before
+      // submitting. The form pre-adds an "empty primary" contact row
+      // for convenience; reps who only want to record a name shouldn't
+      // be forced to either fill it or delete it.
+      const cleanedContacts = (data.contacts ?? []).filter(
+        (c) => typeof c.value === 'string' && c.value.trim().length > 0,
+      );
+      if (cleanedContacts.length === 0) {
+        // The API still requires ≥1 contact. The form-level required
+        // marker on the email input also fires HTML5 validation; this
+        // is the fall-back if the rep wiped the value after focus.
+        throw Object.assign(new Error('At least one contact is required.'), { status: 400 });
+      }
+      // If none of the remaining contacts is flagged primary, promote
+      // the first one — guards against a rep removing the originally-
+      // primary row and leaving an orphan set.
+      if (!cleanedContacts.some((c) => c.isPrimary)) {
+        cleanedContacts[0]!.isPrimary = true;
+      }
+      const payload: CreateClientInput = { ...data, contacts: cleanedContacts };
+
       if (isEdit) {
         // eslint-disable-next-line @typescript-eslint/no-unused-vars
-        const { contacts, tagIds: tIds, ...rest } = data;
+        const { contacts, tagIds: tIds, ...rest } = payload;
         await apiFetch(`/api/v1/clients/${client!.id}`, { method: 'PATCH', body: rest });
         if (tIds) {
           await apiFetch(`/api/v1/clients/${client!.id}/tags`, {
@@ -187,7 +208,7 @@ export function ClientForm({
           });
         }
       } else {
-        await apiFetch('/api/v1/clients', { method: 'POST', body: data });
+        await apiFetch('/api/v1/clients', { method: 'POST', body: payload });
       }
     },
     onSuccess: () => {