feat: Change license from MIT to Apache-2.0

- Added LICENSE.md file with Apache License 2.0 text.
- Created NOTICE file for attribution of third-party components.
- Updated README.md to reflect the new license and included details about the Apache-2.0 license.
- Documented the license change in the diary entry for July 12, 2026.
- Updated installation instructions in getting-started.md to reflect per-user installation.
- Added reusable license header to all source files.
- Updated various documentation files to mention the new Apache-2.0 license.
- Changed legal mentions in example content to reflect the new license.

src/MarkdownConsoleRenderer.cs

@@ -1,3 +1,7 @@
+// Copyright 2026 GitCover Commons gUG (haftungsbeschränkt)
+// Author: Axel Druschel
+// SPDX-License-Identifier: Apache-2.0
+
 using System.Text;
 using System.Text.RegularExpressions;
 using Markdig;