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/__manifest__.py

@@ -3,7 +3,7 @@
 # License OPL-1
 {
     'name': 'Fusion Helpdesk Central — Client API Keys',
-    'version': '19.0.1.1.0',
+    'version': '19.0.1.2.0',
     'category': 'Productivity',
     'summary': 'Admin UI on the central Odoo for issuing per-client API '
                'keys used by fusion_helpdesk client deployments.',
@@ -29,6 +29,7 @@ Depends only on `helpdesk`. No client-side install needed.
         'security/ir.model.access.csv',
         'data/ir_config_parameter_data.xml',
         'data/mail_template_ack.xml',
+        'data/helpdesk_tag_critical.xml',
         'views/fusion_helpdesk_client_key_views.xml',
         'views/helpdesk_ticket_views.xml',
     ],