Add CodeMirror file viewer highlighting

package.json

@@ -16,9 +16,18 @@
     "start:sessiond": "tsx src/server/sessiond.ts"
   },
   "dependencies": {
+    "@codemirror/lang-css": "^6.3.1",
+    "@codemirror/lang-go": "^6.0.1",
+    "@codemirror/lang-html": "^6.4.11",
+    "@codemirror/lang-javascript": "^6.2.5",
+    "@codemirror/lang-json": "^6.0.2",
+    "@codemirror/lang-markdown": "^6.5.0",
+    "@codemirror/lang-python": "^6.2.1",
+    "@codemirror/lang-rust": "^6.0.2",
     "@earendil-works/pi-coding-agent": "^0.74.0",
     "@fastify/static": "^8.3.0",
     "@fastify/websocket": "^11.2.0",
+    "codemirror": "^6.0.2",
     "fastify": "^5.6.1",
     "lit": "^3.3.1",
     "marked": "^18.0.3",