feat(swa): move info button to sidebar foot with matching styling

[Ryback2501]

Summary

• Move the About/information button out of the header and into the foot of the left sidebar, giving it the same look and feel as the other sidebar rail buttons while keeping its existing behaviour (opens the info modal).

Changes

SWA (swa/)

• index.html — remove the info button from the header bar; add it as the last child of the sidebar as a .sidebar-btn with a stroke SVG info icon matching the sibling buttons. Keeps id="info-btn", aria-label/title="About"; no data-section so it is not a section switch.
• app.js — scope the section-navigation query to .sidebar-btn[data-section] so the info button is not wired as a section switcher (no active state, no showSection).
• style.css — remove the now-unused .info-btn rules; add .sidebar-btn-foot { margin-top: auto } to pin the button to the bottom of the rail and a small padding-bottom on the sidebar.

Test plan

• Sign in and confirm the info button sits at the bottom of the sidebar, visually matching the other rail buttons (size, hover, icon style).
• Click it and confirm the info modal opens; close via the × button, backdrop click, and Escape.
• Confirm the four section buttons (User/Relays/Chats/Feeds) still switch sections and the info button never becomes "active".