Collapsible Left Sidebar Improvements

[jondricek]

Summary

Make the left sidebar on desktop both resizable (drag the separator) and collapsible to a compact icon-only column (maybe 60px) so the main content fluidly expands to fill the freed horizontal space.

The mobile overlay/top-collapsed behavior should remain unchanged as it already collapses the sidebar content at the top of each page.

Things to do

• A visible toggle control collapses/expands the sidebar; toggle exposes aria-expanded and aria-controls.
• When collapsed on desktop the sidebar reduces to a compact icon-only column (≈60px) and the main content immediately fills the freed width.
• A resizer handle between sidebar and content allows horizontal drag resizing; enforce min/max width (e.g., 200px–520px) and persist the last width. This is already partially completed, but does not have min/max width set anywhere yet.
• Persist collapsed state and last width across page navigations (suggested localStorage keys: "sidebarCollapsed" and "sidebarWidth").

Files to review / reference:

• Template: attack-theme/templates/general/sidebar-template.html
• Layout template: attack-theme/templates/general/two-column.html
• Stylesheet: attack-theme/static/style-attack.css (built from SCSS files in attack-style/ project)
• Existing resizer script reference: /theme/scripts/resizer.js (as used in attack-theme/templates/general/two-column.html)
• Suggested new script: /theme/scripts/sidebar.js