feat(fusion_helpdesk): customer follow-up + embedded ticket inbox

Squash-merge of feat/helpdesk-customer-followup. The billing and
fusion_login_audit work from that branch is already on main (landed
separately); this lands only the helpdesk feature.

- Identity keystone: submit() forwards partner_email/partner_name/
  x_fc_client_label so the central Helpdesk find-or-creates the customer
  partner and subscribes them as a follower (enables reply emails + magic link).
- Embedded in-app 'My Tickets' inbox: server-side scoped read/reply RPC
  endpoints, per-user seen tracking (fusion.helpdesk.ticket.seen), systray
  unread badge. Defense-in-depth scope domain + _norm_email normalisation
  (wildcard emails cannot widen scope).
- fusion_helpdesk_central: x_fc_client_label field + list/search views +
  branded acknowledgement email template.
- Deployed and smoke-tested live: nexa central 19.0.1.1.0, entech client
  19.0.1.4.1 (requires Contact Creation on the central service account).

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

fusion_helpdesk/models/__init__.py

@@ -1,2 +1,3 @@
 # -*- coding: utf-8 -*-
 from . import res_config_settings
+from . import fusion_helpdesk_ticket_seen

fusion_helpdesk/models/fusion_helpdesk_ticket_seen.py

@@ -0,0 +1,66 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Nexa Systems Inc.
+# License OPL-1
+"""Per-user read-tracking for the embedded ticket inbox.
+
+Stores ONLY metadata — which central ticket a user has seen and up to
+which message id. No ticket content is replicated locally; this exists
+purely so the systray unread badge can work without re-fetching the
+whole inbox on every page load. Tickets themselves remain a live RPC
+view of the central Odoo.
+"""
+from odoo import api, fields, models
+
+
+class FusionHelpdeskTicketSeen(models.Model):
+    _name = 'fusion.helpdesk.ticket.seen'
+    _description = 'Fusion Helpdesk — per-user read tracking (metadata only)'
+
+    user_id = fields.Many2one(
+        'res.users', required=True, index=True, ondelete='cascade',
+        default=lambda self: self.env.uid,
+    )
+    central_ticket_id = fields.Integer(
+        string='Central Ticket ID', required=True, index=True,
+        help='helpdesk.ticket id on the central Odoo.',
+    )
+    last_seen_message_id = fields.Integer(
+        string='Last Seen Message ID', default=0,
+        help='Highest central mail.message id this user has viewed for '
+             'the ticket. Drives the unread badge.',
+    )
+
+    _user_ticket_uniq = models.Constraint(
+        'UNIQUE(user_id, central_ticket_id)',
+        'One seen-row per user per ticket.',
+    )
+
+    @api.model
+    def _mark_seen(self, central_ticket_id, last_message_id):
+        """Upsert the current user's last-seen marker for a ticket.
+
+        Monotonic — never moves the marker backwards (a stale client
+        reporting an older id can't resurrect an unread badge)."""
+        rec = self.search([
+            ('user_id', '=', self.env.uid),
+            ('central_ticket_id', '=', central_ticket_id),
+        ], limit=1)
+        if rec:
+            if (last_message_id or 0) > rec.last_seen_message_id:
+                rec.last_seen_message_id = last_message_id
+        else:
+            self.create({
+                'central_ticket_id': central_ticket_id,
+                'last_seen_message_id': last_message_id or 0,
+            })
+        return True
+
+    @api.model
+    def _seen_map(self, central_ticket_ids):
+        """Return {central_ticket_id: last_seen_message_id} for the
+        current user across the given ticket ids."""
+        rows = self.search([
+            ('user_id', '=', self.env.uid),
+            ('central_ticket_id', 'in', list(central_ticket_ids)),
+        ])
+        return {r.central_ticket_id: r.last_seen_message_id for r in rows}