Editor type scales for real: drop prosekit typography.css, fix selectors

The earlier rem override never matched: editor.mount() turns the
.prosekit-editor div itself into the .ProseMirror root, so
'.prosekit-editor .ProseMirror p' selected nothing and prosekit
typography.css's fixed 16px kept winning. Verified by mounting the
editor standalone and reading the mount div's classes.

Rather than out-specificity a stylesheet we don't control, stop
loading it: prosekit's typography.css is optional px-based sugar. Our
own rem scale (now selected as direct children of .prosekit-editor)
plus UA em defaults for lists/blockquote/code is the whole editor
typography, all tracking the responsive root.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

prosekit-editor.js

@@ -285,8 +285,11 @@ function buildToolbar(editor) {
 }
 
 export function mountEditor(container, hiddenInput, initial) {
+  // Only the structural stylesheet (placeholder, lists, gap cursor).
+  // Deliberately NOT prosekit/basic/typography.css: it sizes content in
+  // fixed px, which fights the app's responsive root font-size. All
+  // editor typography lives in our own stylesheet, in rem.
   ensureStylesheet('https://esm.sh/prosekit/basic/style.css')
-  ensureStylesheet('https://esm.sh/prosekit/basic/typography.css')
 
   const extension = union(
     defineBasicExtension(),