Port the compact page-tree indentation tweak from the docmost-app
WebKit wrapper (previously applied via injected CSS) into the source.
- doc-tree.tsx: change the default `indentPerLevel` prop from 16 to 8,
giving an 8px step per nesting level for a more compact page tree.
No callers override the value, so the single default change applies
everywhere DocTree is rendered. EE-hiding injections from docmost-app
were skipped: those surfaces are already removed in this community fork.
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