feat(fusion_helpdesk): Critical flag, KPI cards, colored stage pills

Three coordinated changes on top of the section grouping:

1. **Mark as Critical** — a red chip on the New tab sets priority='3'
   when submitted. The central post-create hook auto-applies a "Critical"
   helpdesk.tag (shipped via fusion_helpdesk_central data XML, noupdate=1
   so support can recolor without losing it on upgrade), giving support
   a kanban-groupable signal that doesn't rely on remembering what
   priority='3' means. Scoped to in-app-channel tickets only, so a
   support agent manually setting Urgent on their own ticket isn't
   silently tagged.

2. **KPI cards above the sections** — Total / Open / Closed / Critical
   in a 4-up grid (auto-collapses to 2x2 under 540px). Each card uses
   its own saturated gradient so it reads on both light and dark mode —
   the dialog backdrop is irrelevant because the gradient brings its
   own background. Counts are computed in JS from state.tickets so they
   always match what's rendered below.

3. **Colored stage pills** — red Critical, green Solved, dark-yellow New,
   orange Cancelled, blue for In Progress / Testing / On Hold. Critical
   priority gets a *separate* red pill alongside the stage pill so you
   keep stage info even on escalated tickets. Stage matching is
   substring-based (lowercased) so a renamed "Resolved" or "Done" stage
   on central still maps to the green pill.

Tests cover the new is_critical=True → priority='3' wiring and the
default omission so SLA / stage defaults keep working for normal
tickets. Bumps fusion_helpdesk to 19.0.1.7.0 and
fusion_helpdesk_central to 19.0.1.2.0. End-to-end smoke test verified
live: priority=3 + x_fc_client_label triggers the Critical tag.

fusion_helpdesk_central/models/helpdesk_ticket.py

@@ -28,8 +28,34 @@ class HelpdeskTicket(models.Model):
     def create(self, vals_list):
         tickets = super().create(vals_list)
         tickets._fc_send_ack_email()
+        tickets._fc_auto_tag_critical()
         return tickets
 
+    def _fc_auto_tag_critical(self):
+        """Auto-apply the Critical tag on in-app tickets that were filed with
+        priority='3' (Urgent — the client-side "Mark as Critical" toggle).
+
+        Scoped to tickets carrying `x_fc_client_label` so support staff who
+        manually set priority='3' on their own internal tickets aren't
+        silently tagged. Best-effort: if the data XML hasn't loaded the tag
+        yet (e.g. partial install), skip without raising — the ticket is
+        already filed with priority='3' which is the load-bearing signal."""
+        critical = self.filtered(
+            lambda t: t.priority == '3' and t.x_fc_client_label
+        )
+        if not critical:
+            return
+        tag = self.env.ref(
+            'fusion_helpdesk_central.tag_critical', raise_if_not_found=False,
+        )
+        if not tag:
+            _logger.warning(
+                'fusion_helpdesk_central: tag_critical not found, skipping '
+                'auto-tag on %s critical ticket(s).', len(critical),
+            )
+            return
+        critical.write({'tag_ids': [(4, tag.id)]})
+
     def _fc_send_ack_email(self):
         """Send the branded acknowledgement (with magic link) to the customer.