Extract isomorphic @getpaseo/highlight package with syntax-highlighted file preview

- Create packages/highlight with shared Lezer-based syntax highlighting (types, parsers, highlighter, color maps)
- Add syntax highlighting and line numbers to file-pane.tsx with memoized CodeLine component
- Import shared highlight colors in git-diff-pane.tsx instead of local definitions
- Delete duplicated syntax-highlighter.ts from both app and server
- Fix TSX dialect to "ts jsx" (correct per Lezer docs)

package.json

@@ -4,6 +4,7 @@
   "private": true,
   "workspaces": [
     "packages/expo-two-way-audio",
+    "packages/highlight",
     "packages/server",
     "packages/app",
     "packages/relay",
@@ -56,10 +57,10 @@
     "release:major": "npm run version:all:major && npm run release:check && npm run release:publish && npm run release:push"
   },
   "devDependencies": {
-    "prettier": "^3.5.3",
     "get-port-cli": "^3.0.0",
     "knip": "^5.82.1",
     "patch-package": "^8.0.1",
+    "prettier": "^3.5.3",
     "react": "19.1.4",
     "react-dom": "19.1.4",
     "typescript": "^5.9.3"
@@ -81,6 +82,7 @@
     "react-dom": "19.1.4"
   },
   "dependencies": {
-    "@anthropic-ai/claude-agent-sdk": "^0.2.11"
+    "@anthropic-ai/claude-agent-sdk": "^0.2.11",
+    "@modelcontextprotocol/sdk": "^1.27.1"
   }
 }