Verify packaged desktop runtimes across platforms

[czyt]

Summary

• Verify mounted macOS DMG resources and expose the pinned JVM library path to Linux AppImage's dependency scan.
• Smoke extracted Linux deb, rpm and AppImage packages: worker dispatch, exact JRE inventory and offline Dubbo worker.
• Spool rpm2cpio output before cpio reads it, avoiding a producer-side broken pipe and retaining decode errors.
• Restore the exact pinned JRE after linuxdeploy mutates AppImage ELF files. Repack with a SHA256-pinned appimagetool and the original AppImage runtime, then extract and verify the finished package. Refuse sidecar or embedded signatures until signing runs after repacking.

Evidence

• Old run 38946817315 reached package smoke: deb passed, pipe-based RPM extraction returned a hidden producer error. Its exact RPM was downloaded and independently extracted; JRE and Dubbo resources are intact.
• Its AppImage was extracted locally. linuxdeploy had changed JRE ELF hashes while Java still started. Restoring original JRE files and repacking with the pinned plugin produced an AppImage that passed worker, exact JRE/JVM and Dubbo checks.
• Run 38963507351 reached the new repair step, where CI's global APPIMAGE_EXTRACT_AND_RUN=1 made an AppImage runtime signature query return 101. The same environment caused 101 locally. The repair script now clears that variable only for runtime metadata queries; a local full repair with it set passed.
• Run 38972262886 at b575231 is validating the corrected repair and full platform matrix. Superseded failed runs were canceled after logs/artifacts were retained.

Keep this PR in draft until current package smoke and required platform jobs pass. Local Arch lacks Ubuntu desktop libraries, so packaged Linux GUI binary launch is verified by CI.