feat: add note search to sidebar

[j4rviscmd]

Summary

• Replace the "Scripta" title with a full-width search input in the sidebar header
• Filter notes by title in real-time with a 300 ms debounce
• Preserve the timeline group layout (Today / Yesterday / Previous 7 Days / Older) while filtering
• Display an empty state with search term when no notes match

Changes

File	Description
src/features/sidebar/hooks/useDebounce.ts	New generic debounce hook
src/features/sidebar/ui/NoteSidebar.tsx	Search input, title filtering, empty state, extracted renderSidebarBody
src/features/sidebar/index.ts	Re-export useDebounce via public API

Test plan

• Verify search input appears in sidebar header with Search icon and Plus button
• Type a query and confirm notes are filtered by title instantly
• Verify timeline groups are preserved during filtering
• Clear search with X button and confirm all notes reappear
• Verify empty state shows when no notes match the query
• Verify delete and context menu still work correctly

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