feat(shell-plugin): rename login to provider-login (keep login alias)

[tusharmath]

Summary

Rename the shell command :login to :provider-login while preserving :login as a backward-compatible alias, aligning command naming with the Object-Action convention.

Context

Shell commands are moving toward a consistent Object-Action naming format. The existing :login command did not follow this convention, which made command naming less uniform across the plugin.

Changes

• Renamed the built-in command from login to provider-login in command metadata
• Kept backward compatibility by exposing login as an alias
• Updated the dispatcher command pattern to accept both provider-login and login
• Added command naming guidance and alias behavior to shell-plugin documentation

Key Implementation Details

• Built-in command metadata now declares:
  • command: "provider-login"
  • description: "Login to a provider [alias: login]"
• Dispatcher routing now matches provider-login|login and maps both to _forge_action_login
• README now documents the Object-Action naming convention and the backward-compatible alias behavior

Use Cases

• Users can adopt the clearer :provider-login command name
• Existing users relying on :login continue to work without disruption
• Future command additions have clearer naming guidance and consistency

Testing

1. Run the shell plugin and execute :provider-login to verify it triggers provider login flow.
2. Execute :login to verify alias behavior still triggers the same login flow.
3. Run :tools (or command listing) and confirm provider-login is shown with alias metadata.

Links

• Related issues: N/A