feat(ui): add CodeBlock and CodeEditor components with Monaco and hljs

- add CodeBlock for read-only syntax-highlighted display (hljs, js/json)
- add CodeEditor wrapping Monaco editor with theme sync, focus state, and error state
- replace code textareas in snippet, credential, and step pages with CodeEditor
- replace code <pre> blocks in snippet and credential detail pages with CodeBlock
- make form cards full-width on pages with code editors
- add resize:vertical support to CodeEditor wrapper with automaticLayout

client/package.json

@@ -14,6 +14,8 @@
     "format": "prettier --write \"src/**/*.{ts,tsx}\" \".storybook/**/*.{ts,tsx}\""
   },
   "dependencies": {
+    "@monaco-editor/react": "^4.7.0",
+    "highlight.js": "^11.11.1",
     "i18next": "^26.0.4",
     "lucide-react": "^1.7.0",
     "moment": "^2.30.1",