Add GitHub Actions workflows for CI and NuGet publishing, remove Travis CI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: andrei-m-code

.github/workflows/ci.yml

@@ -0,0 +1,22 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [master]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '9.x'
+
+      - name: Restore
+        run: dotnet restore CorePush.sln
+
+      - name: Build
+        run: dotnet build CorePush.sln --no-restore

.github/workflows/publish.yml

@@ -0,0 +1,28 @@
+name: Publish to NuGet
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '9.x'
+
+      - name: Restore
+        run: dotnet restore CorePush.sln
+
+      - name: Build
+        run: dotnet build CorePush.sln --no-restore -c Release
+
+      - name: Pack CorePush
+        run: dotnet pack CorePush/CorePush.csproj --no-build -c Release -o out
+
+      - name: Push to NuGet
+        run: dotnet nuget push out/*.nupkg --api-key ${{ secrets.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate