feat: an as-char frame sits where the file says it does

ODF style:vertical-pos/-rel on an inline frame, which every LibreOffice
formula image carries: baseline, character area, or a plain offset from the
baseline. The default moves from the line-box bottom to the baseline, so a
line with a picture in it keeps the descent below it, as LibreOffice and
Word both do.

src/styles/editor.css

@@ -274,7 +274,9 @@
 .paper .tiptap .image-node {
   position: relative;
   display: inline-block;
-  vertical-align: bottom;
+  /* An as-char frame stands on the text baseline in LibreOffice and Word alike; the
+     file may say otherwise, and image.ts then overrides this per frame. */
+  vertical-align: baseline;
   line-height: 0;
 }
 /* While selected, lift the node (and its handles) above the header/footer layer