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>

utils/rtcLog.ts

@@ -0,0 +1,22 @@
+/** Minimal debug logger for WebRTC / room signaling. Filter console by: sejong-rtc */
+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)
+}
+
+/** Summarize ICE candidate for logs without dumping full SDP. */
+export function iceSummary(candidate?: RTCIceCandidateInit | null) {
+  if (!candidate?.candidate) return { endOfCandidates: true }
+  const parts = candidate.candidate.split(' ')
+  return {
+    type: parts[7] || '?',
+    protocol: parts[2] || '?',
+    address: parts[4] || '?',
+    port: parts[5] || '?',
+  }
+}