Ephemeral extensions persisted to config when resuming sessions

[wpfleger96]

When resuming a session that had ephemeral extensions (via --with-extension), they get permanently saved to config when restored.

Reproduce:

goose session --with-extension "uvx mcp_gdrive@latest"
# ... do work ...
goose session --resume --session-id <id>
# Prompt: "Extension(s) mcpgdrive_sgoMpj77 from previous session are no longer in config. Re-add them to config?"
# Answer: Yes

Check ~/.config/goose/config.yaml - now has a duplicate garbage extension entry like mcpgdrive_sgoMpj77.

Expected: Extensions added via --with-extension should stay ephemeral when resuming - restore for the session only, not save to config.