Add "Reauthenticate" button to SAML error dialogs

[Copilot]

When SAML authentication fails, users currently see an error dialog with only an "OK" button. Clicking it either disables the extension entirely or continues with reduced functionality. Users must reload VS Code to retry authentication.

Changes

Added retry capability to SAML error handling:

• Both SAML error dialogs now include a "Reauthenticate" button alongside "OK"
• Clicking "Reauthenticate" triggers a new SAML authentication flow via showSamlMessageAndAuth()
• Successful reauthentication allows the extension to continue initialization

Implemented retrySamlAuth() helper function:

• Encapsulates retry authentication logic to avoid duplication
• Returns repositories that still lack SAML access after retry

Different success criteria by scenario:

• Full failure (all repos): Requires complete success to proceed
• Partial failure (some repos): Accepts any improvement and continues with available repositories

// Before
await vscode.window.showErrorMessage('SAML access was not provided...', { modal: true });

// After  
const choice = await vscode.window.showErrorMessage(
  'SAML access was not provided...', 
  { modal: true }, 
  reauthenticate
);
if (choice === reauthenticate) {
  const stillMissingAfterRetry = await retrySamlAuth(stillMissing);
  // Continue if successful...
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add "Reauthenticate" button to SAML error</issue_title>
<issue_description>From @joyceerhl:

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add "Reauthenticate" button to SAML error #4471

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