fix(translator): preserve Anthropic web search tools

[0YHR0]

Description
Preserve Anthropic's web_search_20260209 tool when an OpenAI-compatible chat-completions request is routed to an Anthropic backend. The translator now retains the tool name and maps it to Anthropic's built-in web search parameter instead of silently dropping it.

Fixes #2124

Testing

• go test ./internal/apischema/openai ./internal/translator ./internal/extproc -count=1

[0YHR0]

@nacx I refreshed this PR onto the current main history and verified go test ./internal/translator ./internal/apischema/openai -count=1. It fixes #2124 by preserving Anthropic web search tools during Anthropic-to-OpenAI request translation. Could you please review it?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.06%. Comparing base (25afc17) to head (e3d6323).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2355   +/-   ##
=======================================
  Coverage   85.05%   85.06%           
=======================================
  Files         159      159           
  Lines       22645    22653    +8     
=======================================
+ Hits        19261    19269    +8     
  Misses       2217     2217           
  Partials     1167     1167           

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