feat(comment): tighten the comments panel density

The Comments panel was sparse: 12px inner/outer paddings per thread, a
16px gap between avatar and body, body text at the global 16px ProseMirror
size. On a narrow aside column this ate vertical space - few comments per
screen, lots of air.

Tighten strictly inside features/comment (the shared aside frame is left
untouched, so TOC/Details tabs keep their padding):

- Thread Paper: p='sm'->p='xs', mb='sm'->mb='xs' (12->10px).
- Reply-editor Divider: my={4}->my={2}.
- CommentListItem outer Box: pb='xs'->pb={6}; the header Group
  (avatar + body) gains gap='xs' (16->10px).
- Font hierarchy: author name sm->xs (14->12px, fw=500 kept), selection
  quote sm->xs; comment body via a scoped CSS override on
  .commentEditor .ProseMirror: font-size sm (14px) + line-height 1.4,
  margin-top 10->4. The page editor is unaffected (the override is
  scoped to the comment editor module).
- Selection quote padding 8->6, margin-top 4->2.
- Dropped the unused .wrapper rule (no references).

apps/client/src/features/comment/components/comment.module.css

@@ -1,15 +1,11 @@
-.wrapper {
-    padding: var(--mantine-spacing-md);
-}
-
 .focused-thread {
     border: 2px solid #8d7249;
 }
 
 .textSelection {
-    margin-top: 4px;
+    margin-top: 2px;
     border-left: 2px solid var(--mantine-color-gray-6);
-    padding: 8px;
+    padding: 6px;
     background: var(--mantine-color-gray-light);
     cursor: pointer;
     overflow-wrap: break-word;
@@ -32,6 +28,9 @@
         box-shadow: 0 0 0 2px var(--mantine-color-blue-3);
     }
 
+    /* Denser comments: override the global 16px ProseMirror body size with 14px
+       and tighten the rhythm vs. the comment header. Scoped to the comment
+       editor only - the page editor is unaffected. */
     .ProseMirror :global(.ProseMirror){
         border-radius: var(--mantine-radius-sm);
         max-width: 100%;
@@ -39,7 +38,9 @@
         word-break: break-word;
         padding-left: 6px;
         padding-right: 6px;
-        margin-top: 10px;
+        font-size: var(--mantine-font-size-sm);
+        line-height: 1.4;
+        margin-top: 4px;
         margin-bottom: 2px;
     }