fix: configure Image extension as block-level to match Docmost's schema

Closes #4

When update_page contained images, they were silently dropped because
the Image extension was configured with inline: true, but Docmost's
editor uses inline: false, group: "block". The Yjs merge discarded
mismatched inline image nodes.

Fixes PR #5 from the original repo.

src/lib/tiptap-extensions.ts

@@ -11,7 +11,7 @@ export const tiptapExtensions = [
     heading: {},
   }),
   Image.configure({
-    inline: true,
+    inline: false,
   }),
   Link.configure({
     openOnClick: false,