fix(client): compact page tree + fix selection highlight alignment

Reduce DocTree row stride from 32px to 26px for a denser sidebar tree,
and fix the selection/hover highlight that looked unbalanced at the
tighter spacing.

Root causes:
- The virtualized <li> had no explicit height, so `.node`'s height:100%
  collapsed to content height; combined with the asymmetric
  `[role="treeitem"] { padding-bottom: 2px }` rule, row content was
  pushed to the top of the highlight pill (icon glued to the top edge).
- NodeMenu / CreateNode action icons used the default Mantine ActionIcon
  size (md = 28px), overflowing the tighter 26px row stride onto
  neighbouring rows.

Changes:
- doc-tree.tsx: rowHeight 32 -> 26; give each row <li> a definite
  height = rowHeight.
- tree.module.css: rowWrapper fills the slot (height:100%); node pill is
  inset and vertically centered (height: calc(100% - 4px)); drop the
  asymmetric [role="treeitem"] padding-bottom.
- space-tree-node-menu.tsx / space-tree-row.tsx: action icons size={20}.
- share.module.css: drop now-dead .treeNode padding-bottom override.

Verified in an isolated browser harness: highlight content is centered
(2.8/2.8px) and nothing overflows the row stride.

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

@@ -10,7 +10,6 @@
 .treeNode {
   text-decoration: none;
   user-select: none;
-  padding-bottom: 0;
 }
 
 .navbar,