✨ Add typed JVM dialog parents

[vinceglb]

Summary

• replace the AWT-only JVM parentWindow setting with one canonical typed FileKitDialogParent
• support AWT windows, native Windows HWNDs, X11 window IDs, and Wayland surface handles
• route parents through Windows, XDG portal, Linux fallback, AWT/Swing, macOS, and Compose integrations with explicit validation and redacted errors
• demonstrate Nucleus + Tao parenting on Windows and propagate the parent transform through file, directory, and save flows
• document the breaking migration, backend support matrix, borrowed-handle lifetime rules, and Nucleus limitations

This intentionally makes a breaking JVM API change to keep the model simple: callers migrate from parentWindow = window to parent = FileKitDialogParent.awt(window) (or the matching native factory).

Requested from the Kotlin Slack discussion to improve integration with Nucleus using the Tao backend.

Validation

• ./gradlew :filekit-dialogs:jvmTest :filekit-dialogs-compose:jvmTest --no-daemon
• ./gradlew :filekit-dialogs:check :filekit-dialogs-compose:check --no-daemon
• ./gradlew :sample:shared:check :sample:nucleusApp:compileKotlin --no-daemon
• ./gradlew check --no-daemon (572 tasks)
• changed Kotlin sources formatted with ktlint 1.8.0
• two-pass independent GPT-5.6 Sol High implementation review: approved with no substantive standards or spec findings

Manual verification

Windows runtime verification should confirm that the Nucleus Tao sample passes its borrowed HWND to native dialogs and preserves owner-relative modality/stacking. This macOS host cannot execute that Windows-only smoke test.

The Nucleus packaging task could not run locally because the configured Android Studio JBR does not include jpackage; compilation is green and hosted CI uses Temurin JDK 21.