Implements #17, #18, #19, #20, #21
- Add CSS custom properties for density-dependent spacing (--d-* vars)
in theme.css with comfortable (default) and compact modes
- Create useDensity hook with localStorage persistence and DOM attribute sync
- Add FOUC prevention in main.tsx (sync density before first paint)
- Create shared PageFooter component merging stats + pagination
- Refactor AppShell to flex layout with density toggle button (COM/CMP)
- Consolidate inline pagination from ItemsPage/AuditPage into PageFooter
- Delete FooterStats.tsx (replaced by PageFooter)
- Replace all hardcoded padding/font/gap values in ItemTable, AuditTable,
ItemsToolbar, and AuditToolbar with var(--d-*) references
Comfortable mode is already tighter than the previous hardcoded values.
Compact mode reduces further for power-user density.
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