feat: initialize Geekeey Arcade .NET SDK repository

Single-commit squash of the repository history containing the Arcade
.NET MSBuild SDK packages (base, Razor, Web, Test), their analyzer and
editorconfig configuration, test suites, and CI workflows.

.forgejo/workflows/ci.yml

@@ -0,0 +1,79 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+    tags: ['*']
+  pull_request:
+    branches: [main]
+
+enable-openid-connect: true
+
+jobs:
+  build:
+    name: build
+    runs-on: debian-latest
+    container: mcr.microsoft.com/dotnet/sdk:10.0@sha256:0d99ebf1ccad15037b5c98c9fe8979d6b8dbac23812feae2277a0b277b5c5ffa
+    steps:
+      - name: checkout
+        uses: https://code.geekeey.de/actions/checkout@54953ce9d6c7d0a9cbd89d185c5b2c7515358c5f # 1
+
+      - name: dotnet pack
+        shell: bash
+        env:
+          TAG: ${{ forgejo.ref }}
+          TAG_NAME: ${{ forgejo.ref_name }}
+        run: |
+          set -euo pipefail
+
+          if [[ "$TAG" == refs/tags/* ]]; then
+            version="${TAG_NAME#v}"
+            if ! printf '%s' "$version" | grep -Eq '^[0-9]+\.[0-9]+\.[0-9]+$'; then
+              echo "::error::Tag '$TAG_NAME' is not a valid release version (expected MAJOR.MINOR.PATCH)"
+              exit 1
+            fi
+            export version
+          fi
+
+          dotnet pack arcade.slnx
+
+      - name: upload packages
+        uses: https://code.geekeey.de/actions/artifacts/push@ae8d20e174a8706675e6d54ebd3719a2802ea9dd # 1
+        with:
+          name: nuget-packages
+          path: artifacts/package/release
+          pattern: |
+            *.nupkg
+            *.snupkg
+
+      - name: dotnet test
+        run: dotnet test src/sdk.tests/Geekeey.Arcade.NET.Tests.csproj
+
+      - name: publish to nuget
+        if: startsWith(forgejo.ref, 'refs/tags/')
+        shell: bash
+        env:
+          AUDIENCE: "u:1:00000000-0000-0000-0000-000000000000"
+        run: |
+          set -euo pipefail
+
+          if [[ -z "${ACTIONS_ID_TOKEN_REQUEST_URL:-}" || -z "${ACTIONS_ID_TOKEN_REQUEST_TOKEN:-}" ]]; then
+            echo "::error::OpenID Connect is not enabled. Set enable-openid-connect: true on the workflow or job."
+            exit 1
+          fi
+
+          response=$(curl --fail --silent --show-error \
+            --header "Authorization: bearer ${ACTIONS_ID_TOKEN_REQUEST_TOKEN}" "${ACTIONS_ID_TOKEN_REQUEST_URL}&audience=${AUDIENCE}")
+          token=$(printf '%s' "${response}" | grep --only-matching '"value":"[^"]*"' | cut --delimiter '"' --fields 4)
+
+          if [[ -z "${token}" ]]; then
+            echo "::error::Failed to obtain an OpenID Connect token from Forgejo."
+            exit 1
+          fi
+
+          echo "::add-mask::${token}"
+
+          feed="${{ forgejo.server_url }}/api/packages/${{ forgejo.repository_owner }}/nuget/index.json"
+
+          dotnet nuget add source --name forgejo --username forgejo-publish --password "$token" --store-password-in-clear-text "$feed"
+          dotnet nuget push "artifacts/package/release/*.nupkg" "artifacts/package/release/*.snupkg" --source forgejo --skip-duplicate