chore: Migrate from GitHub to Forgejo

- Update repository URL to kitux.de/forgejo/dschlueter/ntu
- Replace GitHub badges with simple repository link
- Update email addresses: dieter.schlueter@linix.de -> dschlueter@kitux.de
- Update all installation and clone instructions
- Update bug report and documentation URLs in manpage
- Mark GitHub Actions workflows as legacy

release.md

@@ -31,8 +31,8 @@ cargo install NameToUnix
 ### Manueller Build
 
 ```bash
-git clone https://github.com/username/NameToUnix.git
-cd NameToUnix
+git clone https://kitux.de/forgejo/dschlueter/ntu.git
+cd ntu
 cargo build --release
 ```
 
@@ -658,7 +658,7 @@ fn main() -> Result<()> {
 ```
 
 
-## 8. ./github/workflows/build.yaml -- GitHub Actions Workflow für CI/CD
+## 8. .github/workflows/build.yaml -- CI/CD Workflow (Legacy)
 
 ```yaml
 name: Build and Test