Three faults from moving the switch into the app sidebar:
1. Clicking Assistant did nothing. activateTab() bailed unless a matching
.tab-btn existed, and removing the "AI Assistant" nav entry removed exactly
that — so every /assistant visit fell through to the fallback tab. A tab
reached from the mode switch legitimately has a section without a button, so
activateTab now keys off the section and only touches the button if present.
2. The switch overflowed its box. The sidebar is 210px; without min-width:0 the
two buttons refused to shrink below their content. They now shrink, with a
slightly tighter font and gap so both labels fit.
3. "Hide menu" had no way back. The toggle sits inside the sidebar it collapses,
so it disappeared with it. It now leaves the collapsing box and pins itself
beside the content, in both the app sidebar and the assistant rail, and the
label already flips to "Show menu".
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WjVc5oaAaYFNbZGLeJp6TX