PE-8433 Add named CLI configuration profiles

[splits-gerard]

Description

Add named CLI contexts that keep saved credentials, API URL, and local EOA together while preserving v1 config behavior.

Changes made

• Add auth profiles create|select|list and SPLITS_PROFILE process selection.
• Isolate API credentials, URLs, and signing keys by profile; env credentials still win.
• Report the active profile in auth whoami and document MCP usage.
• Add legacy/profile-isolation/config-precedence coverage.

How has this been tested?

1. pnpm build
2. pnpm test
3. Created two temporary profiles and verified each creates/removes its own local EOA.

Other notes

Closes PE-8433.

Prompted by: Discord thread