feat: support Anthropic Messages vision requests

[Anionex]

Summary

• Add native VISION_API_PROTOCOL=anthropic support to the shared vision client.
• Translate data URLs and remote image URLs into Anthropic Messages image blocks.
• Send x-api-key and anthropic-version headers instead of Bearer auth in Anthropic mode.
• Default to omitting the thinking field for model compatibility; allow explicit omit, disabled, or adaptive through VISION_ANTHROPIC_THINKING.
• Join only response text blocks and ignore thinking blocks.
• Retry Anthropic 529 overload responses and honor bounded Retry-After values.
• Document the protocol, base-URL rule, authentication behavior, and thinking configuration in English and Chinese.

Verification

• python3 -m py_compile vision_proxy.py vision_client.py ground.py detect.py bin/glance bin/trace bin/crop
• python3 tests/test_vision_client.py
• python3 tests/test_anthropic_rewrite.py
• git diff --check
• GitHub CI: Python 3.11, Python 3.14, Windows egress, and extensions passed on the first revision; rerun pending for the follow-up compatibility/retry commit.

This is a non-UI HTTP-client change; the affected request and retry paths are exercised by the local HTTP fixture in tests/test_vision_client.py.

Follow-up for Anionex/dsh-vision-toolkit#7.

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