Improves build and agent guidelines

Removes outdated Copilot instructions and associated workflow.
Updates common build properties to dynamically set the copyright year.
Refreshes agent guidelines with detailed coding standards, testing practices, and security considerations for contributors.
Adds a copilot setup workflow.

Author: niemyjski

.github/copilot-instructions.md

@@ -0,0 +1,29 @@
+name: "Copilot Setup"
+
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Setup .NET Core
+        uses: actions/setup-dotnet@v5
+        with:
+          dotnet-version: |
+            8.0.x
+            9.0.x
+            10.0.x