Disable PIT mutation testing workflow pending local stabilisation

Rename pit.yml to .disabled so GitHub Actions ignores it. Remove PIT
badge and mention from ReadMe. The pit target and local tooling remain
available in build.xml for continued local development.

Made-with: Cursor

Author: dbenn

.github/workflows/pit.yml .github/workflows/pit.yml.disabled.github/workflows/pit.yml renamed to .github/workflows/pit.yml.disabled

@@ -3,11 +3,10 @@
 [![Snapshot release](https://github.com/AAVSO/VStar/actions/workflows/daily-release.yml/badge.svg)](https://github.com/AAVSO/VStar/actions/workflows/daily-release.yml)
 [![CodeQL](https://github.com/AAVSO/VStar/actions/workflows/codeql.yml/badge.svg)](https://github.com/AAVSO/VStar/actions/workflows/codeql.yml)
 [![SpotBugs](https://github.com/AAVSO/VStar/actions/workflows/spotbugs.yml/badge.svg)](https://github.com/AAVSO/VStar/actions/workflows/spotbugs.yml)
-[![PIT Mutation Testing](https://github.com/AAVSO/VStar/actions/workflows/pit.yml/badge.svg)](https://github.com/AAVSO/VStar/actions/workflows/pit.yml)
 [![Checker Framework](https://github.com/AAVSO/VStar/actions/workflows/checkerframework.yml/badge.svg)](https://github.com/AAVSO/VStar/actions/workflows/checkerframework.yml)
 [![ascl:1407.013](https://img.shields.io/badge/ascl-1407.013-blue.svg?colorB=262256)](https://ascl.net/1407.013)
 
-**[Project Health Dashboard](https://aavso.github.io/VStar/)** — coverage reports, static analysis, mutation testing
+**[Project Health Dashboard](https://aavso.github.io/VStar/)** — coverage reports, static analysis
 
 ## VStar