redesign sidebars, menu, and sidebar search

[JakubKrc]

Layout

• added top bar with external links (hubleto.eu, Reddit, Stack Overflow, LinkedIn, Community, GitHub, guide cross-link)
• Content and sidebars now sit in the middle of the page instead of being stuck to the screen edges
• Old header (with breadcrumbs) and footer bar removed

Sidebar

• Soft radial-gradient background replacing the hard border
• Active page shown as a primary-color left accent line (not filled button)
• toggle arrow — clicking it opens/closes the tree without navigating; clicking the text still navigates
• Smooth slide-down animation on expand/collapse
• Sections you manually open stay open across page navigations (localStorage)

Live sidebar search

• Type 2+ characters → non-matching items dim, matching items highlighted in primary color, parent chain auto-expands

• X button to clear, "Press Enter for full search" placeholder hint

• Inline bg-*-50 card headers in framework/erp/core-architecture pages updated to dark-theme tones