fix: sanitize tool input_schema for Anthropic adapter

[qinlinwang]

Summary

When using Anthropic as the provider, any tool whose input_schema
contains a top-level oneOf/anyOf/allOf causes the API to reject
the entire request with HTTP 400:

Anthropic API error (HTTP 400 Bad Request invalid_request_error):
tools.1.custom.input_schema: input_schema does not support oneOf,
allOf, or anyOf at the top level

This makes the Anthropic provider completely unusable whenever a tool
definition includes composition constraints - which is the case for
several built-in tools.

Root cause: The Anthropic adapter (crates/tui/src/client/anthropic.rs)
passes tool.input_schema to the API as-is, without sanitizing
top-level composition keywords. The OpenAI Responses adapter
(crates/tui/src/client/responses.rs:596-611) already solves this by
calling schema_sanitize::sanitize_for_responses, which:

1. Strips root-level oneOf/anyOf/allOf
2. Merges alternative properties into the root object
3. Surfaces dropped constraints as a description note so the model
   still knows which parameters are expected

Fix: Apply the same sanitize_for_responses call in the Anthropic
adapter before sending tool definitions, aligning both adapters for
consistent schema handling across providers.

Testing

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features
• cargo test --workspace --all-features

Checklist

• Updated docs or comments as needed
• Added or updated tests where relevant
• Verified TUI behavior manually if UI changes
• Harvested/co-authored credit uses a GitHub numeric noreply address

[github-actions]

Thanks @qinlinwang for taking the time to contribute.

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