fix(vision): read auxiliary model from config.yaml before env var

[liuhao1024]

What does this PR do?

The vision_analyze and video_analyze tool handlers read the auxiliary model name exclusively from environment variables (AUXILIARY_VISION_MODEL / AUXILIARY_VIDEO_MODEL), ignoring the auxiliary.vision.model and auxiliary.video.model settings in config.yaml. This creates a routing inconsistency: the gateway's Telegram/WhatsApp image path reads from config correctly (via run_agent.py → vision_analyze_tool), but the direct tool-call path (_handle_vision_analyze → vision_analyze_tool) does not.

This PR makes both handlers prefer config.yaml settings with the env var as a legacy fallback, matching the pattern already used for auxiliary.vision.timeout and auxiliary.vision.temperature in the same file.

Related Issue

Fixes #53749

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• tools/vision_tools.py — _handle_vision_analyze: read auxiliary.vision.model from config.yaml before falling back to AUXILIARY_VISION_MODEL env var
• tools/vision_tools.py — _handle_video_analyze: read auxiliary.video.model (falling back to auxiliary.vision.model) from config.yaml before falling back to env vars
• tests/tools/test_vision_tools.py — added test_config_yaml_model_takes_priority_over_env and test_env_var_used_when_config_missing_model

How to Test

1. Run python -m pytest tests/tools/test_vision_tools.py::TestHandleVisionAnalyze -xvs — all 7 tests should pass
2. Set auxiliary.vision.model: some-model in config.yaml and AUXILIARY_VISION_MODEL=different-model in env → call vision_analyze tool → should use some-model (from config), not different-model (from env)
3. Remove auxiliary.vision.model from config.yaml, keep env var → should fall back to env var value

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS 26.4.1

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

[teknium1]

Merged via PR #57651 alongside #50685. Your commit was cherry-picked onto current main with your authorship preserved in git log (rebase-merge). We adapted the two config-priority tests to the now-async _handle_vision_analyze and gated the native fast path off so they exercise the legacy path they assert on. Thanks!