fix: prevent and recover from JWT token corruption in keyring storage

[ramya18101]

🔧 Changes

Problem: JWT access tokens stored in keyring chunks were getting corrupted, causing cryptic authentication failures like "invalid character 'e' looking for beginning of object value". This happened because old token chunks weren't cleared before storing new ones, leading to contaminated token reconstruction.

Solution:

• Prevention: Clear all existing token chunks before storing new tokens to eliminate contamination
• Recovery: Added JWT validation using proper parsing libraries and enhanced error messages with actionable recovery steps
• User Experience: Replaced cryptic errors with clear guidance like "Your authentication token appears corrupted. Please run: auth0 login"

Methods Changed:

• StoreAccessToken() - Now clears old chunks before storing new tokens
• ValidateAccessToken() - New method for JWT validation using proper parsing
• initializeManagementClientWithTokenValidation() - Enhanced error handling with styled messages

📚 References

• Fixes [QUESTION] Missing scope? auth0-samples/auth0-acul-samples#52
  Also highlighted this issue in one of the older ESD and product-queries

🔬 Testing

Manual Testing:

• Tested authentication flow with corrupted tokens to verify error message clarity
• Verified successful token storage and retrieval after chunk clearing implementation
• Confirmed ANSI styling works correctly in terminal output

📝 Checklist

• [] All new/changed/fixed functionality is covered by tests (or N/A)
• [] I have added documentation for all new/changed functionality (or N/A)

[Copilot]

Pull Request Overview

This PR fixes JWT token corruption issues in keyring storage by implementing prevention and recovery mechanisms. The corruption was caused by old token chunks not being cleared before storing new ones, leading to contaminated token reconstruction and cryptic authentication errors.

Key changes:

• Added chunk clearing logic in StoreAccessToken() to prevent token contamination
• Implemented JWT validation with proper error handling and user-friendly messages
• Enhanced authentication flow with token validation before API client initialization

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
internal/keyring/keyring.go	Added token validation, chunk clearing logic, and JWT parsing functionality
internal/cli/management.go	Enhanced management client initialization with token validation and styled error messages
internal/cli/cli.go	Updated to use new token validation during authentication setup

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[kushalshit27]

Please check the comment by the review bot before merging the PR