DMY-66: fix upgrades from receipt-owned OpenGUI MCP installations

[HarveySang]

The public WorkBuddy installer rejects prior OpenGUI HTTP installations because its ownership check only recognizes stdio arguments. DMY-66 adds recognition using the native installation receipt's configuration root, transport and exact server fingerprint. Recognized HTTP entries migrate to the public package's stdio transport with stale URL and authorization fields removed.

Unknown or edited entries fail before configuration writes. The error names the configuration file, supplies quoted backup/editor commands, and explains how to preserve the existing server under an unused key before retrying.

Validation:

• Reproduced MCP_CONFLICT with the new isolated regression fixture on the original installer, then observed it pass after the fix.
• Build and runtime validation pass; 61 test files / 497 unit tests pass.
• Installer regression passes: owned HTTP migration, prior stdio upgrade, repeat install and six preserved conflict cases.
• Existing install tests pass, including backups, configuration-root migration and symlink rejection.

The user's WorkBuddy configuration was inspected read-only. WorkBuddy was not restarted. This PR updates the installer source shipped as opengui-mcp/scripts/install-local.mjs; public release artifacts still need rebuilding and publishing after merge.