windows: harden config and credential path handling

[shrey16]

Goal

Harden Windows path handling for credentials and local engine config.

Cases to cover

• user profile path contains spaces
• configured project path contains spaces
• config directory does not exist yet
• credential file already exists with safe permissions

Acceptance

• Tests cover Windows-style paths without needing a real Windows runner.
• No visible copy changes are required unless an error message becomes clearer.
• The CLI does not print token values or private paths beyond the local config path a user already controls.