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/js/service_booking/service_booking.js

@@ -25,8 +25,10 @@ export class ServiceBookingWizard extends Component {
         onWillStart(async () => {
             const r = await rpc("/fusion_claims/service_booking/refdata", {});
             Object.assign(this.state, {
-                technicians: r.technicians, calloutRates: r.callout_rates,
-                perKm: r.per_km, labour: r.labour,
+                technicians: r.technicians || [],
+                calloutRates: r.callout_rates || [],
+                perKm: r.per_km ?? 0.70,
+                labour: r.labour || this.state.labour,
             });
         });
     }
@@ -59,9 +61,13 @@ export class ServiceBookingWizard extends Component {
         this.state.device = ev.target.value;
         this.state.category = ev.target.value === "lift" ? "lift" : "standard";
     }
+    onCallType(ev) {
+        const r = this.state.calloutRates.find(x => x.code === ev.target.value);
+        if (r) { this.state.category = r.category; this.state.timing = r.timing; }
+    }
     setCust(m) { this.state.custMode = m; }
-    setTiming(t) { this.state.timing = t; }
     setAmpm(v) { this.state.ampm = v; }
+
     toggleInShop() { this.state.inShop = !this.state.inShop; }
     _timeStartFloat() { return (this.state.hour % 12) + (this.state.ampm === "PM" ? 12 : 0) + this.state.minute / 60; }