v1.25.4 - Pack login: keychain-stored sessions

Fixes enigma <pack> asking to log in when the account's real token is stored in the OS keychain (Claude Code on Windows), not in a file.

In that case the account's .credentials.json is blank; the pack was copying that empty file into its isolated context, which blocked the agent from resolving its own session and forced a login. Seeding now copies only a usable token and otherwise leaves the context untouched, so the agent resolves the login itself (keychain) - or you sign in once and the isolated context remembers it.

Ships enigma-cli@1.25.4.