fix(study): 캔버스 디버그 오버레이 제거 (좌표 표시 거슬림)

frontend/src/lib/components/HandwriteCanvas.svelte

@@ -79,9 +79,6 @@
   const WIDTH_FACTOR: Record<Width, number> = { thin: 0.6, normal: 1, thick: 1.6 };
   let effectiveSize = $derived(baseSize * WIDTH_FACTOR[widthMode]);
 
-  // 디버그: 캔버스 크기 + 마지막 pointer 정보. 좌표 어긋남 디버깅용.
-  let lastDebug = $state<{x:number;y:number;p:number;t:string} | null>(null);
-
   // 지우개 반경 (CSS px) — effectiveSize 의 약 4배. Apple Pencil 정밀도와 균형.
   let eraserRadius = $derived(Math.max(16, effectiveSize * 4));
 
@@ -246,7 +243,6 @@
 
     activePointerId = e.pointerId;
     const [x, y] = getLocalXY(e);
-    lastDebug = { x: Math.round(x), y: Math.round(y), p: e.pressure, t: e.pointerType };
 
     if (tool === 'eraser') {
       const removed = eraseAt(x, y);
@@ -269,7 +265,6 @@
   function onPointerMove(e: PointerEvent) {
     if (e.pointerId !== activePointerId) return;
     const [x, y] = getLocalXY(e);
-    lastDebug = { x: Math.round(x), y: Math.round(y), p: e.pressure, t: e.pointerType };
 
     if (tool === 'eraser') {
       const removed = eraseAt(x, y);
@@ -512,12 +507,5 @@
       style="touch-action: none; cursor: {tool === 'eraser' ? 'cell' : 'crosshair'};"
     ></canvas>
 
-    <!-- 디버그 오버레이 — 좌표 어긋남 디버깅 후 제거 예정 -->
-    <div class="absolute top-1 right-1 px-2 py-1 rounded bg-bg/80 text-[10px] text-dim font-mono pointer-events-none">
-      {cssWidth}×{cssHeight}
-      {#if lastDebug}
-        · {lastDebug.t} ({lastDebug.x},{lastDebug.y}) p={lastDebug.p.toFixed(2)}
-      {/if}
-    </div>
   </div>
 </div>