feat: add OAuth credential type to add identity TUI wizard

[aidandaly24]

Description

Add OAuth credential type to the agentcore add identity TUI wizard. Previously, the interactive wizard only supported API Key credentials — users had to use CLI flags (--type oauth) for OAuth. This PR adds OAuth as a selectable option in the TUI.

When the user selects OAuth, the wizard collects:

• Credential name
• OIDC discovery URL (validated to end with /.well-known/openid-configuration)
• Client ID (masked input)
• Client secret (masked input)
• Scopes (optional, comma-separated)

The confirm screen shows the appropriate fields for each type. Both paths use the existing createCredential operation — no changes to the operations layer or CLI.

New wizard flows:

• API Key: type → name → apiKey → confirm
• OAuth: type → name → discoveryUrl → clientId → clientSecret → scopes → confirm

Related Issue

N/A — prerequisite for CUSTOM_JWT inbound auth (Task 17)

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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