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_central/models/__init__.py

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

fusion_helpdesk_central/models/helpdesk_ticket.py

@@ -0,0 +1,57 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Nexa Systems Inc.
+# License OPL-1
+"""Central-side helpdesk.ticket extensions for the customer follow-up flow.
+
+Adds the `x_fc_client_label` deployment tag (set by the in-app reporter so
+the embedded inbox can scope per client) and sends a branded acknowledgement
+email — carrying the portal magic link — when an in-app ticket is created.
+"""
+import logging
+
+from odoo import api, fields, models
+
+_logger = logging.getLogger(__name__)
+
+
+class HelpdeskTicket(models.Model):
+    _inherit = 'helpdesk.ticket'
+
+    x_fc_client_label = fields.Char(
+        string='Client Deployment', index=True, copy=False,
+        help='Deployment tag (e.g. ENTECH) set by the fusion_helpdesk in-app '
+             'reporter. Scopes the embedded "My Tickets" inbox per client and '
+             'lets support filter tickets by originating deployment.',
+    )
+
+    @api.model_create_multi
+    def create(self, vals_list):
+        tickets = super().create(vals_list)
+        tickets._fc_send_ack_email()
+        return tickets
+
+    def _fc_send_ack_email(self):
+        """Send the branded acknowledgement (with magic link) to the customer.
+
+        Only fires for in-app-channel tickets (those tagged with a client
+        label) that have a customer email — external web-form submissions
+        rely on the native website confirmation, so this won't double-send.
+        The whole thing is best-effort: a template/mail failure must never
+        block ticket creation, so we log and move on.
+        """
+        template = self.env.ref(
+            'fusion_helpdesk_central.mail_template_ticket_ack',
+            raise_if_not_found=False,
+        )
+        if not template:
+            return
+        for ticket in self:
+            if not (ticket.x_fc_client_label and ticket.partner_email):
+                continue
+            try:
+                template.send_mail(ticket.id, force_send=False)
+            except Exception:  # noqa: BLE001 — ack must never block create
+                _logger.exception(
+                    'fusion_helpdesk_central: acknowledgement email failed '
+                    'for ticket %s (%s)', ticket.id, ticket.x_fc_client_label,
+                )