Refactor examples into per-app directories with separate HTML, CSS, and JS

- Give each example its own directory: chat/, whiteboard/, sdk-demo/, hrpc-demo/, data-demo/, screenshare/
- Split each into index.html, style.css, and app.js (no inline script/style; CSP-friendly)
- Remove old flat files (e.g. chat.html, whiteboard.html, whiteboard.js)
- Update README, examples/README, and docs/HRPC to use new paths

examples/chat/style.css

@@ -0,0 +1,58 @@
+* { box-sizing: border-box; }
+body {
+  font-family: system-ui, -apple-system, sans-serif;
+  max-width: 560px;
+  margin: 0 auto;
+  padding: 1rem;
+  background: #1a1b26;
+  color: #c0caf5;
+  min-height: 100vh;
+}
+h1 { font-size: 1.25rem; margin: 0 0 1rem; color: #7aa2f7; }
+.row { display: flex; gap: 0.5rem; margin-bottom: 0.75rem; align-items: center; }
+input[type="text"] {
+  flex: 1;
+  padding: 0.5rem 0.75rem;
+  border: 1px solid #3b4261;
+  border-radius: 6px;
+  background: #24283b;
+  color: #c0caf5;
+  font-size: 0.95rem;
+}
+input::placeholder { color: #565f89; }
+button {
+  padding: 0.5rem 1rem;
+  border: none;
+  border-radius: 6px;
+  font-size: 0.9rem;
+  cursor: pointer;
+  font-weight: 500;
+}
+button.primary { background: #7aa2f7; color: #1a1b26; }
+button.primary:hover { background: #89b4fa; }
+button.primary:disabled { opacity: 0.5; cursor: not-allowed; }
+button.danger { background: #f7768e; color: #1a1b26; }
+button.danger:hover { background: #ff9db5; }
+.status {
+  font-size: 0.85rem;
+  color: #9ece6a;
+  margin-bottom: 0.5rem;
+}
+.status.error { color: #f7768e; }
+.log {
+  background: #24283b;
+  border: 1px solid #3b4261;
+  border-radius: 6px;
+  padding: 0.75rem;
+  height: 220px;
+  overflow-y: auto;
+  font-family: ui-monospace, monospace;
+  font-size: 0.8rem;
+  line-height: 1.4;
+  margin-top: 1rem;
+}
+.log .peer { color: #bb9af7; }
+.log .msg { color: #9ece6a; }
+.log .sys { color: #7aa2f7; }
+.log .err { color: #f7768e; }
+.peers { font-size: 0.85rem; color: #a9b1d6; margin-bottom: 0.5rem; }