Split repository guidance into directory READMEs

[akriaueno]

Summary

• keep the root README focused on the repository overview and directory layout
• add templates/README.md for the template catalog and usage instructions
• keep example-specific information in examples/README.md
• simplify the directory README titles to Templates and Examples

Validation

• verified every relative link in the three affected README files
• confirmed all 11 templates and both examples are linked from their respective directories
• ran git diff --check

Note

The SonarCloud workflow fails before analysis because its token cannot query JRE metadata. This is the same existing authentication failure seen on develop and is unrelated to this documentation-only change.