Fix material editor launch diagnostics

[durswd]

Summary

Fix Material Editor launch failures that could appear as a no-op when opening .efkmat files.

• Recenter saved window positions when the Material Editor would otherwise restore off-screen
• Report and log Material Editor launch failures instead of silently swallowing exceptions
• Detect immediate process exits and IPC command failures
• Increase the material path IPC buffer and avoid sending truncated paths

Fixes #1169.

Testing

• dotnet build Dev\Editor\Effekseer\Effekseer.csproj
• cmake --build build --config Release --target EffekseerMaterialEditor Viewer
• git diff --cached --check