fix(ai_agents): enforce TLS certificate verification

[yaodong-shen]

Summary

• keep default certificate and hostname verification in six cloud WebSocket clients
• add an AST regression test that scans production extensions for disabled TLS verification
• run the security invariant from the top-level ai_agents test task and document the TLS policy

Fixes #2230

Scope

The issue identified three affected clients. A repository-wide scan found the same insecure pattern in stepfun_tts_python, xfyun_asr_python, and xfyun_asr_dialect_python, so this PR fixes all six production occurrences.

Validation

• uvx --python 3.12 --from pytest pytest -q ai_agents/tests/test_tls_verification.py
• Python 3.12 compileall for all changed Python files
• Black check for the new test and changed files without pre-existing formatting drift
• Go Task dry run of ai_agents test, confirming test-security runs before extension and server tests
• local self-signed TLS handshake test, confirming the default context rejects an untrusted certificate
• git diff --check

The full containerized extension suite could not be run locally because Docker is unavailable; repository CI will exercise that environment.

[yaodong-shen]

The claude-review check failed before reviewing the diff because the workflow requires the PR actor to have repository write permission:

Actor has insufficient permissions: read
Action failed with error: Actor does not have write permissions to the repository

This is an external fork PR, so I cannot resolve or rerun that repository-side workflow. The branch is currently mergeable with no conflicts. Could a maintainer rerun or exempt this check for external contributors?

[yaodong-shen]

In addition to the claude-review permission failure noted above, the Lint PR Name, Lint Commit Messages, Build Docker Image for AI Agents, CodeQL Analysis, and AI Agents (Build & Test) workflows are all waiting for maintainer approval and created no jobs for this external-fork PR. The focused TLS regression, compile, formatting, and handshake validations pass locally. Could a maintainer approve those workflow runs as well when convenient?