1.2.2: timeline duration handle + frame-snapped script frames + cleaner time display

- Duration grip at the right edge of the scrub ruler. Drag to
  resize the active timeline (clip duration in clip-edit, scene
  duration otherwise); maps clientX → seconds and snaps to the
  scene's frame grid before calling setDuration. Hidden in button-
  asset edit (state grid is fixed).
- Script-frame times go through a quantizeToFrame helper at the
  store level (addScriptFrame / setScriptFrameTime / duplicateScriptFrame),
  so drag input no longer produces values like 1.4181818… and the
  playhead lands exactly on the frame during tick().
- Header time and DocumentDrawer duration input now show the
  duration rounded to 2 decimals — frame-aligned floats like
  4.733333… read as 4.73. Setter still writes the user-typed full-
  precision value through unchanged.

package.json

@@ -1,7 +1,7 @@
 {
   "name": "ruwio",
   "private": true,
-  "version": "1.2.1",
+  "version": "1.2.2",
   "type": "module",
   "scripts": {
     "dev": "vite",