Fix shutdown cleanup and prepare 1.0.1

[zzsolt]

Fix the plugin-name shutdown double-free so Notepad++ can exit normally with CSV Visual Editor loaded.

• Use Npp.DotNet.Plugin ownership correctly: assign PluginNamePtr = IntPtr.Zero without manually freeing it first.
• Add production-host clean-exit regression coverage.
• Prepare the 1.0.1 maintenance package and Plugins Admin metadata.

CI #428 passed completely, including normal Notepad++ 8.9.8 x64 shutdown with CleanShutdownObserved=true.

Owner manual Plugins Admin lifecycle on the exact CI #428 candidate:

• Deactivate: PASS
• re-Activate: PASS
• Remove: PASS

Validated package SHA-256: 2405357696cca26f6887701ab6d4e58c7c8671a201796c7a454048b521b29978
Validated DLL SHA-256: f1340be31577ea443199de43844b6170bcd72e05d34229a93f546d973fd542b8

Only the public 1.0.0 -> 1.0.1 update-path check remains before upstream nppPluginList submission.