feat(fusion_helpdesk): group My Tickets into Critical/New/Solved sections

The flat write_date-sorted list was hard to scan with 50+ tickets — solved
ones were intermixed with active ones, and there was no signal for
priority. Bucket each ticket server-side into 'critical' (open + priority
High/Urgent), 'solved' (stage marked fold=True on central) or 'open'
(everything else), and render three labelled sections in the dialog with
sticky headers, count badges, and per-group accent colours. Backend keeps
its write_date desc order so latest is always at top within each bucket.

Bucketing uses helpdesk.stage.fold (not the stage name) so renaming
"Solved" to "Done" on the central won't quietly mis-categorise rows.
Adds bucket_ticket() in utils.py with unit tests covering the
folded-wins-over-priority precedence and the missing-priority fallback.

Also surfaces a small Urgent (triangle) / High (arrow) icon on each row
so a critical ticket reads at a glance even after a user scrolls past
the section header.

Bumps fusion_helpdesk to 19.0.1.6.0.

fusion_helpdesk/__manifest__.py

@@ -3,7 +3,7 @@
 # License OPL-1 (Odoo Proprietary License v1.0)
 {
     'name': 'Fusion Helpdesk Reporter',
-    'version': '19.0.1.5.0',
+    'version': '19.0.1.6.0',
     'category': 'Productivity',
     'summary': 'One-click in-app bug reporting & feature requesting — '
                'auto-creates a helpdesk.ticket on a central Odoo Helpdesk.',