Feature/storage locations followups

[highbyte]

Summary

Implements storage-location follow-ups for user data, snapshots, scripts, settings diagnostics, and host UI discoverability.

Changes

• Standardized snapshot save/load defaults so relative snapshot paths resolve under the shared snapshots directory.
• Added storage-path diagnostics across hosts:
  • Headless/Avalonia Desktop: --show-storage-paths
  • TCP remote control: emu.storagepaths
  • RemoteClient: dotnet-6502-remote emu.storagepaths
  • Lua: emu.storage_paths()
• Exposed effective storage paths in Avalonia Desktop and Terminal UI.
• Documented current storage locations, settings behavior, and follow-up decisions.
• Fixed Avalonia Options dialog issues for snapshot/script path fields and reset behavior.

Verification

• Built affected Headless, RemoteClient, Remoting, Scripting, Systems, Avalonia, and Terminal projects.
• Ran Systems tests.
• Smoke-tested Headless TCP remote save/load snapshot flow.
• Smoke-tested emu.storagepaths and Lua emu.storage_paths().

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud