style: align sidebar nav rows with folder/file row styling

[h4yfans]

What

Align sidebar nav rows (Inbox, Journal, Tasks) with folder/file row styling for visual consistency.

Why

The top-level sidebar nav rows were visually inconsistent with the folder/note rows in the Collections section below. They used a taller, chunkier row primitive while folder/file rows used a tighter tree-node style. This made the nav feel like "bolted-on chrome" instead of a continuous list.

How

Added a single className override to <SidebarMenuButton> in sidebar-nav.tsx:53 that copies the exact tokens from TreeNodeTrigger:

• Height: h-8 → h-7 (32px → 28px)
• Radius: rounded-md → rounded-[5px] (6px → 5px)
• Padding: p-2 → p-0 pl-1 pr-2.5 (asymmetric: 4px left / 10px right)
• Gap: gap-2 → gap-1.5 (8px → 6px)
• Font: text-sm → text-[13px] leading-4 font-medium
• Text color: text-sidebar-foreground

The twMerge conflict resolver picks the later class, so the override cleanly wins. The CVA's [&>svg]:size-4 and hover/active color tokens remain unchanged.

Type

• style — visual/UI only

Test plan

• Manual testing (visual verification: hover, selected state, collapsed rail, dark mode, badge clipping)
• All existing unit + integration tests pass (262 test files, 5,557 tests)
• Lint clean (no new errors)
• Typecheck clean (all packages, contracts, IPC verified)

Checklist

• Self-reviewed the diff
• No hardcoded secrets or credentials
• Single file under 500 LOC (sidebar-nav.tsx is 67 lines)
• Follows immutable data patterns (no state mutations)