chore: remove all temporary debug instrumentation

Investigations are closed, so strip the probes: bzDbg + __perfProbe definitions, the
older/render/slide/pwaFocus call sites, and the server-side /api/dbg (MDBG) sink. Kept
the functional code around each probe (renderThread's innerHTML build, the older-page
re-anchor, the slide fade). No behavior change. build batch153.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/routes.js

@@ -1005,13 +1005,6 @@ try {
 } catch (_) {}
 route('GET', '/api/build', (req, res) => json(res, 200, { build: APP_BUILD }));
 
-// TEMP perf/debug sink — the app POSTs slide frame-timing + scroll state so we diagnose jank from the
-// server log (docker logs bizgaze-support) with real device numbers. Remove once the slide/scroll settle.
-route('POST', '/api/dbg', async (req, res) => {
-  try { const b = await readBody(req); console.log('[MDBG]', JSON.stringify(b)); } catch (_) {}
-  json(res, 200, { ok: true });
-});
-
 // Mint a LiveKit join token for the signed-in user + a specific room (the 6-digit meeting code).
 // The room-membership/host authorization already happens over the meeting WebSocket; this only
 // hands the client a media-plane credential scoped to that room and its own identity.