Move theme, language, and copy switchers to the burger menu (#199)

[Raghaddahi]

Relates to #199

Description

Moves the theme toggle, copy button, and language selector out of .page-tools (above the article content) and into the burger menu overlay on mobile, so they no longer take up space above the content on small screens.

Approach: render the tools in both places (.page-tools in base.html and .primary-nav__tools in navigation.html) and toggle visibility with CSS breakpoints — no JS DOM manipulation. The theme toggle button id was replaced with a .js-theme-toggle class so the JS wires up both instances.

Worth careful review:

• The copy-button Bootstrap dropdown inside the scrollable .primary-nav overlay may clip instead of overlay content on mobile — verify on a narrow viewport.
• page/request were added to the header inclusion-tag context; request is currently unused (kept defensively).

Testing

• before

• After

AI usage

• Agent: AI assisted with the PR description and review only. The code was written by a human; AI reviewed the diff and prepared this description.