feat: classify local command failures and additional API statuses in the JSON error envelope

[developerkunal]

🔧 Changes

Previously, many local command failures returned bare fmt.Errorf/errors.New values that fell through to the generic code: unknown / reason: unclassified in the JSON error envelope. This makes the envelope actionable for agents by classifying local, user-fixable failures with a specific code and reason, without touching the human-facing message text.

• Wrapped local validation failures across auth0 client-grants, auth0 apps, auth0 quickstarts, auth0 network-acl, auth0 guardian, auth0 email, auth0 actions, auth0 roles, auth0 users, auth0 flows, auth0 forms, auth0 login, auth0 terraform generate, auth0 api, and others. Missing required flags, incompatible flag combinations, and invalid flag values now surface as usage; malformed local JSON payloads and other client-side input validation surface as validation.
• auth0 api now classifies its own client-side failures: an invalid method or URI, an unreadable --data file, and empty stdin surface as usage/validation, and a 403 insufficient_scope response surfaces as auth with reason insufficient_scope.
• Widened server-side HTTP status classification: 409 responses now classify as a new conflict code, and 410/415 as validation, instead of falling back to unknown/server_error.

The classification wrappers (usageError, authError, validationError) preserve the original error via Error()/Unwrap(), so errors.Is/errors.As still traverse and the message a human sees is unchanged. Only the envelope code/reason and analytics classification change.

🔬 Testing

• make test-unit passes, including new table rows in exit_test.go for the 409/410/415 class and reason mappings.
• make lint reports no new issues from these changes.
• make docs produces no diff (the change is classification metadata, not command/flag surface).

📝 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)