fix(icom): the 7760 power meter interpolates between MEASURED anchors

A known 50 W read raw ~89 where the two-segment curve said 62: the face is
not linear in watts below half scale. Watts now interpolate through the
measured points (50 W, 100 W, full-scale 250 W); refining the curve is adding
a row to the table.

frontend/src/components/IcomPanel.tsx

@@ -135,10 +135,20 @@ function fmtVFO(hz?: number): string {
 // and raw 213 is full scale. On a real 7760 a measured 100 W sits at half
 // deflection of the 250 W face — the linear ×2.5 first tried showed 140 W for
 // it. Below half scale watts run 0→100, above it 100→250.
+// The anchors are MEASURED on the real radio, not derived: a known 50 W read
+// raw ≈89 and a known 100 W read raw 143 (Icom's documented half-deflection),
+// with raw 213 = full scale = 250 W. The face is not linear in watts at the
+// bottom — a two-segment guess showed 50 W as 62 — so watts interpolate
+// between the measured anchors, and a new measurement just adds a row.
+const ICOM_7760_PO: [number, number][] = [[0, 0], [89, 50], [143, 100], [213, 250]];
 function icomWatts(pct: number): { w: number; defl: number } {
   const raw = Math.max(0, pct * 2.55);
   const defl = raw <= 143 ? (raw / 143) * 50 : Math.min(100, 50 + ((raw - 143) / 70) * 50);
-  const w = raw <= 143 ? (raw / 143) * 100 : Math.min(250, 100 + ((raw - 143) / 70) * 150);
+  let w = 250;
+  for (let i = 1; i < ICOM_7760_PO.length; i++) {
+    const [r0, w0] = ICOM_7760_PO[i - 1], [r1, w1] = ICOM_7760_PO[i];
+    if (raw <= r1) { w = w0 + ((raw - r0) / (r1 - r0)) * (w1 - w0); break; }
+  }
   return { w: Math.round(w), defl };
 }