fix(fusion_claims): OWL wizard review fixes (statement handler, scss borders, tech guard)

- Move the call-type select handler into onCallType() — OWL cannot compile a
  multi-statement inline t-on body (was a render-breaking crash on mount).
- Replace color-mix() inside border shorthands with var(--sb-border) (Odoo-19
  SCSS drops color-mix in a border shorthand).
- Technician placeholder option value '' (not 'false') so the required-tech
  guard isn't bypassed.
- Remove dead setTiming(); null-coalesce the refdata onWillStart load.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fusion_claims/static/src/scss/service_booking.scss

@@ -221,7 +221,7 @@
         align-items: center;
         justify-content: space-between;
         background: var(--sb-money-soft);
-        border: 1px solid color-mix(in srgb, var(--sb-money) 35%, transparent);
+        border: 1px solid var(--sb-border);
         border-radius: 10px;
         padding: 11px 14px;
         margin-top: 4px;
@@ -234,7 +234,7 @@
     .estimate {
         grid-column: 1 / -1;
         background: var(--sb-money-soft);
-        border: 1px solid color-mix(in srgb, var(--sb-money) 40%, transparent);
+        border: 1px solid var(--sb-border);
         border-left: 5px solid var(--sb-money);
         border-radius: 13px;
         padding: 15px 18px;