Phone portrait: a bottom tab bar Drive / Queue / Chat (/ Mod for admins) shows one panel at a time (from main at 1142ee6, forge.json untouched) #159

Replaces #113. Both tries failed in forge.json, not in the change. Pull #116 ran into the check block on main without check.run (main fixed that in 1142ee6). Pull #146 also edited forge.json, so it no longer merges into main. Branch smith/113-phone-portrait-a-bottom-tab-bar-drive-qu has the code; take it without its forge.json change.

Done, at 390x844 and 412x915 portrait:

• [ ] A bottom tab bar, 56 px + env(safe-area-inset-bottom), targets >= 44 px: Drive, Queue, Chat, plus Mod for admins and moderators only. A tap shows that panel and hides the others; the tab is kept in location.hash.
• [ ] The forge pill covers nothing. The bar is hidden on desktop and in landscape. STOP is in no tab.
• [ ] Logic in Software/so101/src/ui/tabs.js (hash -> visible panel), styles in src/ui/tabs.css. src/ui/tabs.test.ts: an unknown hash falls back to Drive; Mod is absent for a plain viewer.
• [ ] Branched from main at 1142ee6 or later; the diff does not touch forge.json. bun --cwd Software/so101 test passes.