feat: markdown rendering for response viewer

Add marked.js (39KB) for rich text display in the response viewer.
Renders headings, code blocks, lists, tables, blockquotes, and
inline formatting with dark theme styling.

Falls back to escaped plain text if marked.js fails to load.

src/web/public/styles.css

@@ -7865,9 +7865,100 @@ kbd {
   color: #51cf66;
 }
 
+/* Markdown rendered content inside response viewer */
 .rv-text {
-  white-space: pre-wrap;
   word-break: break-word;
+  line-height: 1.6;
+}
+
+.rv-text p {
+  margin: 0 0 0.6em;
+}
+
+.rv-text p:last-child {
+  margin-bottom: 0;
+}
+
+.rv-text h1, .rv-text h2, .rv-text h3, .rv-text h4 {
+  color: #e0e0e0;
+  margin: 1em 0 0.4em;
+  line-height: 1.3;
+}
+
+.rv-text h1 { font-size: 1.3em; }
+.rv-text h2 { font-size: 1.15em; }
+.rv-text h3 { font-size: 1.05em; }
+
+.rv-text code {
+  background: #2a2a3e;
+  padding: 1px 5px;
+  border-radius: 3px;
+  font-size: 0.9em;
+}
+
+.rv-text pre {
+  background: #1e1e2e;
+  border: 1px solid #333;
+  border-radius: 6px;
+  padding: 10px 12px;
+  overflow-x: auto;
+  margin: 0.6em 0;
+}
+
+.rv-text pre code {
+  background: none;
+  padding: 0;
+  font-size: 0.85em;
+  line-height: 1.5;
+}
+
+.rv-text ul, .rv-text ol {
+  margin: 0.4em 0;
+  padding-left: 1.4em;
+}
+
+.rv-text li {
+  margin-bottom: 0.2em;
+}
+
+.rv-text blockquote {
+  border-left: 3px solid #444;
+  margin: 0.6em 0;
+  padding: 0.3em 0 0.3em 12px;
+  color: #999;
+}
+
+.rv-text strong {
+  color: #f0f0f0;
+}
+
+.rv-text a {
+  color: #5c7cfa;
+  text-decoration: none;
+}
+
+.rv-text table {
+  border-collapse: collapse;
+  margin: 0.6em 0;
+  width: 100%;
+  font-size: 0.9em;
+}
+
+.rv-text th, .rv-text td {
+  border: 1px solid #333;
+  padding: 4px 8px;
+  text-align: left;
+}
+
+.rv-text th {
+  background: #2a2a3e;
+  color: #e0e0e0;
+}
+
+.rv-text hr {
+  border: none;
+  border-top: 1px solid #333;
+  margin: 1em 0;
 }
 
 .response-viewer-body {
@@ -7879,8 +7970,6 @@ kbd {
   font-size: 13px;
   line-height: 1.5;
   color: #d4d4d4;
-  white-space: pre-wrap;
-  word-break: break-word;
 }
 
 .response-viewer-body:empty::after {