chore: add Copilot cloud sandbox setup and dev container with hve-core-all

.devcontainer/devcontainer.json

@@ -0,0 +1,23 @@
+{
+  "name": "Ziyada (.NET 9)",
+  "image": "mcr.microsoft.com/devcontainers/dotnet:1-9.0-bookworm",
+  "features": {
+    "ghcr.io/devcontainers/features/node:1": {
+      "version": "20"
+    }
+  },
+  "postCreateCommand": "dotnet restore Ziyada.sln && bash .devcontainer/setup-hve-core.sh",
+  "remoteEnv": {
+    "GITHUB_TOKEN": "${localEnv:GITHUB_TOKEN}"
+  },
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "ms-dotnettools.csharp",
+        "ms-dotnettools.csdevkit",
+        "GitHub.copilot",
+        "GitHub.copilot-chat"
+      ]
+    }
+  }
+}

.devcontainer/setup-hve-core.sh

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+#!/usr/bin/env bash
+#
+# setup-hve-core.sh
+#
+# Best-effort, non-fatal, idempotent installation of the GitHub Copilot CLI and
+# the hve-core-all plugin (https://github.com/microsoft/hve-core).
+#
+# This script is shared by:
+#   * the Copilot cloud sandbox setup workflow
+#     (.github/workflows/copilot-setup-steps.yml), and
+#   * the dev container (.devcontainer/devcontainer.json).
+#
+# Every step is best-effort: the sandbox and dev container MUST still start even
+# if the Copilot CLI or the plugin cannot be installed (for example when the
+# environment is offline or the CLI has not been authenticated). Failures are
+# therefore downgraded to warnings and never abort the caller.
+set -euo pipefail
+
+echo "==> [hve-core] Ensuring GitHub Copilot CLI is installed"
+command -v copilot >/dev/null 2>&1 || npm install -g @github/copilot || echo "::warning::copilot CLI install failed"
+
+echo "==> [hve-core] Adding microsoft/hve-core plugin marketplace"
+copilot plugin marketplace add microsoft/hve-core || echo "::warning::marketplace add failed"
+
+echo "==> [hve-core] Installing hve-core-all plugin"
+copilot plugin install hve-core-all@hve-core || echo "::warning::hve-core-all install failed"
+
+echo "==> [hve-core] Installed plugins:"
+copilot plugin list || true
+
+echo "==> [hve-core] Setup script complete"

.github/workflows/copilot-setup-steps.yml

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+name: "Copilot Setup Steps"
+
+# Provisions and validates the GitHub Copilot cloud sandbox for this repository.
+# The Copilot coding agent runs the job named exactly `copilot-setup-steps`
+# before it starts working, so this workflow both bootstraps the sandbox and
+# lets us exercise that bootstrap on demand (workflow_dispatch) or whenever the
+# setup files themselves change.
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+      - .devcontainer/setup-hve-core.sh
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+      - .devcontainer/setup-hve-core.sh
+
+permissions:
+  contents: read
+
+jobs:
+  # The job name MUST be `copilot-setup-steps` for the Copilot coding agent to
+  # discover and run it as the sandbox bootstrap.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
+        with:
+          persist-credentials: false
+
+      # Primary runtime for this repo: .NET 9 (see src/Ziyada/Ziyada.csproj).
+      - name: Setup .NET
+        uses: actions/setup-dotnet@67a3573c9a986a3f9c594539f4ab511d57bb3ce9 # v4.3.1
+        with:
+          dotnet-version: '9.0.x'
+          cache: true
+          cache-dependency-path: '**/*.csproj'
+
+      # Node is required so the Copilot CLI (an npm package) and the
+      # hve-core-all plugin can be installed, even though this is not a Node repo.
+      - name: Setup Node.js
+        uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
+        with:
+          node-version: '20'
+
+      - name: Restore .NET dependencies
+        continue-on-error: true
+        run: dotnet restore Ziyada.sln
+
+      - name: Install hve-core-all plugin
+        continue-on-error: true
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        run: bash .devcontainer/setup-hve-core.sh
+
+      - name: Verify tools
+        run: |
+          echo "OS:        $(uname -srm)"
+          echo ".NET SDK:  $(dotnet --version 2>/dev/null || echo 'not installed')"
+          echo "Node:      $(node --version 2>/dev/null || echo 'not installed')"
+          echo "npm:       $(npm --version 2>/dev/null || echo 'not installed')"
+          echo -n "Copilot:   "; copilot --version 2>/dev/null || echo 'not installed'
+          echo "Copilot plugins:"
+          copilot plugin list 2>/dev/null || echo "  (copilot CLI unavailable)"