fix(panel): KI-272 — PremiumCalculatorPanel copay pre-fill + re-sync on profile load

E1 Playwright run found three pre-fill bugs in PremiumCalculatorPanel that
D1 either missed or that occurred via timing race:

1. **Copay always 0** — D1's derivation helpers covered age/SI/family/PED/
city but copay was hardcoded `useState(0)`. Profile's `copay_pct=20`
never propagated. Fix: `useState<number>(initialProfile?.copay_pct ?? 0)`.

2. **Age stuck at 35, family stuck at "Self only"** — useState initializers
run ONCE on first mount. If profile data loads AFTER the panel mounts
(race: user clicks the chip the moment profile finishes fetching), the
sliders never update. Fix: new useEffect watches `initialProfile` changes
and updates each slider IFF the slider still holds its initial-default
value. Once user moves a slider, future profile updates no longer
override their choice (snapshot-comparison ref prevents redundant runs).

3. **SI now correctly prefers desired_sum_insured_inr over
existing_cover_inr** — already shipped in KI-270 / D1; this commit
also threads it into the re-sync useEffect for parity.

Verification:
- npx tsc --noEmit clean
- Re-sync logic only updates sliders that are still at their initial
default — user's manual changes are preserved.

This pairs with backend KI-271 (SLOT_UNION-driven profile endpoints) — now
the profile loaded by getProfileCompleteness actually contains copay_pct +
family_medical_history + desired_sum_insured_inr, and the panel will
correctly pre-fill from them.

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

frontend/src/app/page.tsx

@@ -2162,10 +2162,50 @@ function PremiumCalculatorPanel({
   const [ped, setPed] = useState<"none" | "diabetes_or_hypertension" | "heart_disease" | "multiple">(
     derivePed(initialProfile?.health_conditions),
   );
-  const [copay, setCopay] = useState(0);
+  // KI-272 — copay pre-fill (D1 missed this). When profile has copay_pct,
+  // start the slider there instead of 0.
+  const [copay, setCopay] = useState<number>(initialProfile?.copay_pct ?? 0);
   const [estimate, setEstimate] = useState<PremiumEstimateResponse | null>(null);
   const [busy, setBusy] = useState(false);
 
+  // KI-272 — re-sync sliders if profile loads AFTER the panel has mounted
+  // (race: user clicks the chip the moment profile data finishes fetching).
+  // We use a "user has not yet touched this slider" guard: only update from
+  // profile when the slider still holds its initial-default value. Once the
+  // user moves a slider, profile updates no longer override their choice.
+  const profileSnapshotRef = useRef<string>("");
+  useEffect(() => {
+    if (!initialProfile) return;
+    const snap = JSON.stringify([
+      initialProfile.age,
+      initialProfile.desired_sum_insured_inr ?? initialProfile.existing_cover_inr,
+      initialProfile.location_tier,
+      initialProfile.dependents,
+      initialProfile.health_conditions,
+      initialProfile.copay_pct,
+    ]);
+    if (snap === profileSnapshotRef.current) return;
+    profileSnapshotRef.current = snap;
+    if (initialProfile.age != null && age === 35) setAge(initialProfile.age);
+    const newSI =
+      initialProfile.desired_sum_insured_inr ??
+      initialProfile.existing_cover_inr;
+    if (newSI != null && sumInsured === 1_000_000) setSumInsured(newSI);
+    if (initialProfile.location_tier && cityTier === "metro") {
+      setCityTier(deriveCityTier(initialProfile.location_tier));
+    }
+    if (initialProfile.dependents && familySize === 0) {
+      setFamilySize(deriveFamilySize(initialProfile.dependents));
+    }
+    if (initialProfile.health_conditions?.length && ped === "none") {
+      setPed(derivePed(initialProfile.health_conditions));
+    }
+    if (initialProfile.copay_pct != null && copay === 0) {
+      setCopay(initialProfile.copay_pct);
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [initialProfile]);
+
   useEffect(() => {
     const handler = setTimeout(() => {
       setBusy(true);