style(ui): polish control sizing and spacing

[ClaudiaFang]

Summary

• normalize search, filter, toolbar, tree, and per-file action control sizing
• use compact 32px desktop controls with 6–8px spacing while preserving narrow-sidebar usability
• establish a clearer action hierarchy: Push uses the Obsidian accent, Pull/Refresh are neutral, and Delete is an outlined destructive action
• provide 44px touch targets for mobile controls and folder disclosure
• switch mobile toolbar and per-file actions to predictable two-column layouts
• keep all changes scoped to the Sync Status view without changing sync behavior

UX rationale

The current toolbar mixes solid green, blue, and red buttons with tight 4px gaps and sub-44px mobile targets. This patch reduces competing emphasis, improves hit areas, and keeps narrow panels legible.

Validation

• CI build passed
• CI lint passed
• tests passed on Node 22 and Node 24
• added focused tests for desktop hierarchy/sizing and mobile touch targets/layout
• manual Obsidian verification is still recommended for default light/dark themes, a narrow sidebar, and mobile portrait/landscape

Refs #86

[sonarqubecloud]

Quality Gate failed

Failed conditions
15.1% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud