refactor(auth): centralize credential storage

[YuMo12268]

Summary

• Introduce a crate-private CredentialStore to centralize credential path resolution and file operations.
• Route Client and Worker JWT cache reads, writes, updates, and removals through CredentialStore.
• Store cached JWTs in a readable normalized_origin,username,token format.
• Scope cached JWTs by normalized Coordinator origin and username.
• Preserve the existing authentication flow and token encoding.
• Do not persist login passwords.
• Initialize the Client credential store during MitoHttpClient construction and share a single credential-loading path between Client and Worker.

Validation

• Added unit tests verifying that:
  • trailing-slash and default-port aliases normalize to the same Coordinator origin;
  • different schemes, hosts, and non-default ports remain distinct;
  • paths, queries, and fragments do not affect Coordinator identity;
  • comma-separated credential entries are parsed correctly.
• Manually verified that:
  • cached tokens use the readable three-field format;
  • cached authentication reuses the existing token without falling back to login;
  • trailing-slash aliases reuse the same cached credential;
  • refresh updates the cached token without appending another record;
  • revoke removes the matching cached token.

[un-lock-able]

Please remember to rebase this branch onto the updated auth-enhancement branch.