Prepare RadioCore_Kit 1.0.0 release

[Quency-D]

What changed

• Rename the Arduino Library Manager package to RadioCore_Kit and set version 1.0.0.
• Replace the public entry header with RadioCore_Kit.h across all examples and documentation.
• Add strict Arduino Library Manager submission linting and tag/version validation.
• Document the controlled manual release process.

Why

This prepares the repository for its first GitHub Release and initial submission to the Arduino Library Manager registry.

User impact

The public include changes from RadioCore.h to RadioCore_Kit.h. No compatibility header is retained, as agreed for the first stable release.

Validation

• Arduino Lint 1.3.0 strict/submit: no errors or warnings.
• git diff --check passed.
• All 10 examples include RadioCore_Kit.h.
• No .development, .exe, symlink, or submodule entries.
• No compilation or hardware testing performed.