Improve content width and add collapsible sidebar

[adulau]

Motivation

• Make body copy more readable by using more of the desktop viewport while keeping comfortable gutters.
• Give readers control to hide the right-hand sidebar to reduce distractions and increase available space for long-form content.
• Persist the reader's layout preference across pages for a consistent reading experience.

Description

• Widen the desktop content container and add a wrapper layout by updating layouts/_default/single.html and layouts/_default/list.html to include a content-container and content-layout region with a toolbar and a toggle button that targets #content-sidebar.
• Add a lightweight, deferred script static/js/sidebar-toggle.js that exposes the toggle, stores the preference in localStorage under misp-content-sidebar-hidden, and applies a .is-sidebar-hidden class to the layout.
• Load the toggle script from layouts/partials/headers.html and add CSS rules in static/css/custom.css to increase the max width to 1420px on large viewports and style the toggle plus the hidden-sidebar behavior so the main column expands when the sidebar is hidden.
• Keep the toggle hidden when JavaScript is unavailable and preserve existing responsive behavior for smaller screens.

Testing

• Ran git diff --check which reported no issues.
• Ran node --check static/js/sidebar-toggle.js which succeeded (no syntax errors).
• Attempted a local Hugo preview, but hugo is not installed in the environment so a full site build could not be validated.
• Attempted to fetch the theme submodule for a local preview, but the environment failed to clone the theme (network proxy returned HTTP 403), so visual verification in-browser was not possible.

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Codex Task

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-29T10:36:21.766868Z	9c80469	PR opened
🔒 Security Review	✅ Completed 2026-09-29T10:36:04.450464Z	9c80469	PR opened

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