fix(cli): send --allow-no-credential to the server

[HouMinXi]

Summary

• providers add --allow-no-credential only skipped the local prompt. The request never carried the flag, and the server schema did not accept it, so a provider that legitimately has no credential was still rejected.
• The request now includes the flag when it was set. The server accepts it only for a provider whose catalog says a credential is optional, and rejects it with 400 otherwise. A request without the flag is checked exactly as before.

Related Issues

• Closes fix(providers): 'providers add --allow-no-credential' never tells the server the connection is credential-optional; 'providers test' then falsely reports 'no API key configured' #15031

Validation

• Change type: other (CLI provider add)
• Focused tests: node --import tsx/esm --test tests/unit/cli/provider-crud.test.ts (15 pass)
• eslint on the changed files, with the repo suppression file
• Reconciled with release/v3.8.52 @ 23a1148486
• Updated test covers the change
• Defect injection: removing the line that writes the flag makes the assertion fail, and the change was restored

Tests Added Or Updated

• tests/unit/cli/provider-crud.test.ts (updated)

Coverage Notes

• The test asserts the flag is present in the body only when set, and absent otherwise.

Reviewer Notes

• buildProviderPayload has one production caller, the add command. The schema rejects the flag for a provider that requires a credential, so the flag cannot be used to skip a real requirement.