fix(fusion_repairs): code-review batch - 4 critical + 8 high + 8 medium/low

Critical
- C1: _sql_constraints -> models.Constraint (Odoo 19 deprecation rule violation)
- C2: variance threshold no longer uses abs() - under-cost is good news,
  must not block invoicing. Now only OVER-cost triggers requires_requote.
- C3: roll_next_due_date() was dead code - now wired from
  fusion.technician.task.write() when a maintenance task transitions to
  'completed', so the whole maintenance lifecycle actually advances.
- C4: warranty.is_active was store=True but time-dependent (became stale).
  Dropped store=True; find_active_for() now filters by expiry_date directly.

High
- H1: added x_fc_maintenance_contract_id back-link on repair.order and
  populated it from create_repair_from_booking().
- H2: find_active_for() returns empty when neither lot nor product is
  supplied - prevents cross-product false warranty matches.
- H3: visit-report wizard now creates stock.move records of repair_line_type
  'add' for each part line, so Odoo's native action_create_sale_order()
  chain has lines to invoice and stock gets consumed properly.
- H4: office intake email template now carries a fallback email_to header
  computed from res.company.x_fc_office_notification_ids (or company email),
  so it does not silently send with no recipient.
- H5: maintenance reminder cron nextcall now always rolls to tomorrow
  at 07:00 local time, so installing/upgrading after 07:00 does not
  immediately fire all the day's reminders.
- H6: public portal no longer hardcodes UID 1 as the intake user fallback
  (which in Odoo 19 is OdooBot). Prefers base.user_admin, else the
  lowest-id non-share user, else SUPERUSER_ID.
- H7: public portal validates client_email via tools.email_normalize
  before partner creation; malformed addresses redirect with error=email.
- H8: find_best_match() returns empty when no symptom keywords match
  (no silent first-catalog guess) and uses word-boundary regex to avoid
  matching 'battery' inside 'no battery problem'.

Medium
- M1: _inherit moved next to _name on maintenance_contract (cosmetic but
  brittle if Odoo refactors model class detection)
- M2: relativedelta(months=N) instead of timedelta(days=N*30) for warranty
  and maintenance intervals (correct month boundaries)
- M3: unique constraint on fusion.repair.maintenance.contract.booking_token
- M6: dispatch task fallback now searches for an actual x_fc_is_field_staff
  user; gracefully skips and logs if no field staff exists (instead of
  silently failing the constraint check)
- M7: maintenance contract list view date decoration uses context_today()
  (date) instead of strftime(string) - the str comparison would TypeError
- M9: Visit Report button hidden on draft repairs and when no technician
  task is linked yet

Low
- L2: portal-created partners get default lang + company_id so mail
  templates render in the right language
- L3: dropped unused exception variable in sales rep portal controller
- L4: visit-report wizard 'found another issue' now redirects to the
  spawned stub repair so the tech can fill it in immediately
- L5: dropped unrecognized data-string from <app> in settings view

Public portal also: rate-limit check moved BEFORE the counter increment so
blocked attempts do not keep inflating the bucket.

All fixes verified end-to-end on local westin-v19:
- variance one-sided: 0.5h labour vs $500 est -> requires_requote=False;
  2h x $250 + $200 parts vs $100 est -> requires_requote=True
- maintenance roll-forward: created MC/00006 due 2026-05-31, completed
  linked maintenance task -> contract rolled to 2026-11-21 with
  last_reminder_band reset
- warranty find_active_for(partner only) -> empty recordset
- service catalog find_best_match with unrelated text -> empty recordset
- pg_constraint shows fusion_repair_maintenance_contract_booking_token_unique
- /repair landing still 200 after restart

Co-authored-by: Cursor <cursoragent@cursor.com>

fusion_repairs/models/repair_order.py

@@ -2,7 +2,7 @@
 # Copyright 2024-2026 Nexa Systems Inc.
 # License OPL-1 (Odoo Proprietary License v1.0)
 
-from datetime import timedelta
+from dateutil.relativedelta import relativedelta
 
 from odoo import api, fields, models, _
 from odoo.exceptions import UserError
@@ -71,6 +71,15 @@ class RepairOrder(models.Model):
         index=True,
         help='Auto-matched catalogue entry that pre-fills estimated cost and duration.',
     )
+
+    # Maintenance contract back-link (Phase 3)
+    x_fc_maintenance_contract_id = fields.Many2one(
+        'fusion.repair.maintenance.contract',
+        string='Maintenance Contract',
+        index=True,
+        help='Set when this repair was spawned from a maintenance reminder booking. '
+             'Completing the related technician task rolls the contract to its next cycle.',
+    )
     x_fc_intake_answer_count = fields.Integer(
         compute='_compute_intake_answer_count',
     )
@@ -240,8 +249,8 @@ class RepairOrder(models.Model):
         )
         if not warranty_months:
             return False
-        # Datetime + months: use simple 30-day approximation per month for now.
-        cutoff = fields.Datetime.from_string(str(delivery_date)) + timedelta(days=warranty_months * 30)
+        # relativedelta handles month boundaries correctly (28/29/30/31).
+        cutoff = fields.Datetime.from_string(str(delivery_date)) + relativedelta(months=warranty_months)
         return fields.Datetime.now() <= cutoff
 
     # ------------------------------------------------------------------