Fix macOS runnable class collisions

[vinceglb]

Summary

• give FileKit's macOS/JVM runnable adapter a FileKit-specific Objective-C class name
• reject null and zero-valued JNA class allocations before native registration
• construct, retain, and use the owned adapter class with safe add/register/dispose ordering
• add native-free lifecycle tests and a real macOS collision regression
• include the approved issue plan and glossary under specs/

Validation

• ./gradlew :filekit-dialogs:jvmTest --tests 'io.github.vinceglb.filekit.dialogs.platform.mac.foundation.ObjcRunnableClassRegistrationTest' --no-daemon
• ./gradlew :filekit-dialogs:jvmTest --tests 'io.github.vinceglb.filekit.dialogs.platform.mac.foundation.FoundationRunnableIntegrationTest' --no-daemon
  • macOS 26.5.2, OpenJDK 21.0.10
  • 1 test executed, 0 skipped
• ./gradlew :filekit-dialogs:check --no-daemon
• focused ktlint 1.8.0 with compose rules 0.6.0
• git diff --check

The local repository-wide check was capacity-limited after approximately 491 tasks by No space left on device; the affected module checks were green before that environmental failure. The complete matrix is covered by this PR's CI.

#626