Sidebar overhaul + dark mode (closes #15, #16, #17, #18, #20)

[PlayerNguyen]

Implements issues #15, #16, #17, #18, #20.

Changes

• Configurable sidebar items via configureSidebar.tsx #15 — Configurable sidebar via src/configs/configureSidebar.tsx
• Sidebar search/filter functionality #16 — Search/filter sidebar items by label + keywords (nested too)
• Sidebar compact/icon-only mode #17 — Compact/icon-only mode (tooltip on hover, centered icons)
• Sidebar footer with cogwell and dropdown menu #18 — Sidebar footer with cogwell Menu dropdown (Settings, Compact toggle, Theme, Logout)
• Dark mode as default theme with light/dark toggle #20 — Dark mode default (defaultColorScheme="dark"), toggle in footer dropdown, persists via Mantine localStorage

New files

• src/types/sidebar.ts — shared AppNavbarLink type
• src/configs/configureSidebar.tsx — nav item config
• AppNavbarLinkGroup.tsx — recursive link renderer with search + compact
• AppNavbarFooter.tsx — footer cogwell + dropdown

Modified files

• AppNavbar.tsx — refactored to use config/sections/search/compact/footer
• DasboardLayout/index.tsx — compact state, dynamic navbar width (60/200px)
• App.tsx — defaultColorScheme="dark"
• Removed hardcoded bg={"dark.1"} on AppShell.Main