feat: add perspective view toggle and update camera handling

js/i18n/en.js

@@ -5,9 +5,11 @@ export default {
   "theme.toggleAriaLabel": "Toggle light/dark mode",
   "dropHint.text": "Drop an <strong>.stl</strong>, <strong>.obj</strong> or <strong>.3mf</strong> file here<br/>or <label for=\"stl-file-input\" class=\"link-label\">click to browse</label>",
   "ui.wireframe": "Wireframe",
+  "ui.perspective": "Perspective View",
   "ui.controlsHint": "Left drag: orbit  ·  Right drag: pan  ·  Scroll: zoom",
   "ui.meshInfo": "{n} triangles · {mb} MB · {sx} × {sy} × {sz} mm",
   "ui.loadStl": "Load Model…",
+  "ui.localProcessingNote": "All processing runs locally in your browser — no data is uploaded.",
   "sections.displacementMap": "Displacement Map",
   "ui.uploadCustomMap": "Upload custom map",
   "ui.noMapSelected": "No map selected",