raise screen share quality and stop the grid from overflowing

Screen share was capped by WebRTC's default ~2.5 Mbps and by window
capture resolution, and fixed aspect-video cards forced the page to
scroll. Adds minimal [sejong-rtc] logs to diagnose ICE failures.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/utils/rtcLog.ts

@@ -0,0 +1,10 @@
+/** Server-side minimal signaling / WebRTC relay logs. */
+export function rtcLog(...args: unknown[]) {
+  // eslint-disable-next-line no-console
+  console.log('[sejong-rtc]', ...args)
+}
+
+export function rtcWarn(...args: unknown[]) {
+  // eslint-disable-next-line no-console
+  console.warn('[sejong-rtc]', ...args)
+}