Clarify login status stored credential wording

[GreyforgeLabs]

Summary

• change stored AuthMode::ApiKey login status wording from "API key" to neutral "stored API credential"
• avoids misleading output after cortex login --token, which shares the same stored auth shape as --with-api-key

Fixes PlatformNetwork/bounty-challenge#53145

Tests

• cargo fmt --package cortex-cli --check
• git diff --check
• cargo check -p cortex-cli --no-default-features --features cortex-tui

Note: package unit tests are currently blocked on main by an unrelated stale private import in src/cortex-cli/src/agent_cmd/tests.rs, so I kept validation to the compiling no-default-features profile used for this change.

[greptile-apps]

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