Initial scaffold: Researcher Endorsement frontend

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/agents/devcontainer.agent.md

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+---
+name: "Devcontainer Generator"
+description: "Scaffolds a VS Code devcontainer (Docker-based) for consistent development environments (Node, Docker, extensions)."
+triggers:
+  - "create devcontainer"
+  - "generate .devcontainer"
+  - "scaffold codespaces container"
+---
+
+# Devcontainer Generator
+
+Purpose
+- Create `.devcontainer/devcontainer.json` and optional Dockerfile to provide a reproducible development experience in Codespaces or local VS Code Remote - Containers.
+
+Example prompts
+- "create devcontainer for node 18 with yarn and Docker socket"
+- "generate container with vscode extensions for react and typescript"
+
+Sample devcontainer.json
+```json
+{
+  "name": "ArXiv Social Dev",
+  "image": "mcr.microsoft.com/vscode/devcontainers/javascript-node:0-18",
+  "features": {
+    "docker-in-docker": "latest"
+  },
+  "postCreateCommand": "npm ci",
+  "customizations": {
+    "vscode": {
+      "extensions": ["esbenp.prettier-vscode", "dbaeumer.vscode-eslint", "ms-vscode.vscode-typescript-next"]
+    }
+  }
+}
+```
+
+Notes
+- Recommend adding Docker socket bind for local containerized builds and Codespaces compatibility.
+- Provide scripts to run `devcontainer` locally and instructions for Codespaces.