feat(viewer2d): 2.5D view, viewport fill transform and Z-aware fit box

- 2.5D view: a toolbar toggle (plus an options-panel checkbox) re-aims the
  orthographic camera at an SE-isometric angle and unlocks orbit, so the
  CAD elevation already in the vertex buffers (contours, TIN, 3D
  polylines) becomes visible. Nothing is re-tessellated; switching back
  restores the locked top view. A Z exaggeration slider (persisted in the
  options store) makes kilometre-wide sheets with metres of relief
  legible; picking and the X/Y readout intersect the Z=0 plane.
- Viewport fills: SOLID/HATCH fills and dimension arrowheads drawn
  through a paper-space VIEWPORT now get the model-to-paper transform
  (_fillXf / _bakeFillXf), as lines already did via pushSeg.
- The trimmed content box keeps the drawing's real Z range instead of
  collapsing to z=0, so the 2.5D fit and clip slab cover the relief.
- src/topProgress.ts: driver for the existing #progress loading bar. It
  is not imported from main.ts yet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.ts

@@ -231,6 +231,7 @@ document.getElementById('theme')!.addEventListener('click', () => {
   viewer.setTheme(dark);
   fillLayers();
 });
+
 // ── 옵션 패널 ────────────────────────────────────────────────────
 // 값은 IndexedDB(hmw-viewer/options)에 남는다. 선가중치 배율은 재파싱 없이
 // 즉시 반영되므로 드래그하면서 화면을 보고 맞출 수 있다.
@@ -242,6 +243,10 @@ const optLwOut = document.getElementById('optLwOut')!;
 const optGrid = document.getElementById('optGrid') as HTMLInputElement;
 const optZoomSpeed = document.getElementById('optZoomSpeed') as HTMLInputElement;
 const optZoomSpeedNum = document.getElementById('optZoomSpeedNum') as HTMLInputElement;
+const opt25D = document.getElementById('opt25D') as HTMLInputElement;
+const optZRow = document.getElementById('optZRow')!;
+const optZScale = document.getElementById('optZScale') as HTMLInputElement;
+const optZScaleNum = document.getElementById('optZScaleNum') as HTMLInputElement;
 
 makePanelDraggableAndCollapsible(optionsPanel, {
   collapseBtnEl: document.getElementById('collapseOptBtn')!,
@@ -295,11 +300,41 @@ function applyZoomSpeed(v: number, persist = true) {
 optZoomSpeed.addEventListener('input', () => applyZoomSpeed(parseFloat(optZoomSpeed.value)));
 optZoomSpeedNum.addEventListener('input', () => applyZoomSpeed(parseFloat(optZoomSpeedNum.value)));
 
+// ── 2.5D 보기 토글 ───────────────────────────────────────────────
+// Top 뷰를 풀고 남동 등각(SE Isometric)으로 기울인다. 도면 정점은 이미 CAD
+// 표고(Z)를 갖고 있으므로 재파싱·재생성 없이 카메라만 돌리면 등고선 같은
+// 높낮이가 그대로 드러난다. 다시 누르면 원래 Top 뷰(회전 잠금)로 돌아온다.
+// 뷰 상태라 IndexedDB 에 저장하지 않는다 — Z 과장 배율만 저장한다.
+const view25Btn = document.getElementById('view25Btn')!;
+
+function apply25D(on: boolean) {
+  viewer.set25D(on);
+  view25Btn.classList.toggle('on', on);
+  view25Btn.textContent = on ? '2.5D 보기 ✓' : '2.5D 보기';
+  opt25D.checked = on;
+  optZRow.classList.toggle('disabled', !on);
+  setStatus(on ? '2.5D 보기 · 왼쪽 드래그=회전, 가운데·오른쪽 드래그=이동' : 'Top 뷰');
+}
+view25Btn.addEventListener('click', () => apply25D(!viewer.is25D()));
+opt25D.addEventListener('change', () => apply25D(opt25D.checked));
+
+function applyZScale(v: number, persist = true) {
+  if (!Number.isFinite(v) || v <= 0) return;
+  viewer.setZScale(v);
+  optZScale.value = String(v);
+  optZScaleNum.value = String(v);
+  if (persist) void setOption('zScale', v);
+}
+optZScale.addEventListener('input', () => applyZScale(parseFloat(optZScale.value)));
+optZScaleNum.addEventListener('input', () => applyZScale(parseFloat(optZScaleNum.value)));
+
 document.getElementById('optReset')!.addEventListener('click', () => {
   viewer.setLineweightScale(null);   // 뷰어 기본 배율
   viewer.setLineweightEnabled(null); // 도면의 LWDISPLAY 를 다시 따름
   viewer.setGrid(false);
   applyZoomSpeed(1);
+  applyZScale(1);
+  apply25D(false);
   optGrid.checked = false;
   void setOption('lineweightScale', null);
   void setOption('lineweightOn', null);
@@ -313,6 +348,7 @@ void getAllOptions().then((o) => {
   if (typeof o.lineweightOn === 'boolean') viewer.setLineweightEnabled(o.lineweightOn);
   if (o.grid === true) { viewer.setGrid(true); optGrid.checked = true; }
   if (typeof o.zoomSpeed === 'number') applyZoomSpeed(o.zoomSpeed, false);
+  if (typeof o.zScale === 'number') applyZScale(o.zScale, false);
   syncOptions();
 });
 syncOptions();