feat(web): add markdown syntax highlighting, slash commands, stop button, quote/reply

- PromptEditor with Prism.js syntax highlighting
- Slash commands (/run, /status, /images, /list, /help) in chat input
- Stop button to cancel ongoing generation
- Quote/reply and regenerate/continue actions in chat
- MiddlePanel with conversation timestamps and preview
- Pipeline progress in chat view
- Fix all remaining dark theme classes

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/client/package.json

@@ -12,14 +12,17 @@
     "clsx": "^2.1.0",
     "lucide-react": "^0.460.0",
     "markdown-it": "^14.1.0",
+    "prismjs": "^1.30.0",
     "react": "^18.3.0",
     "react-dom": "^18.3.0",
     "react-router-dom": "^7.15.0",
+    "react-simple-code-editor": "^0.14.1",
     "tailwind-merge": "^2.6.0",
     "zustand": "^5.0.0"
   },
   "devDependencies": {
     "@types/markdown-it": "^14.1.0",
+    "@types/prismjs": "^1.26.6",
     "@types/react": "^18.3.0",
     "@types/react-dom": "^18.3.0",
     "@types/react-router-dom": "^5.3.3",