fix(tool): include quality fields in output schema

[chaliy]

Motivation

• The FetchResponse now serializes quality fields (word_count, redirect_chain, is_paywall) but the tool's advertised JSON output schema had "additionalProperties": false and omitted these fields, causing strict consumers to reject otherwise valid responses.

Description

• Add word_count, redirect_chain, and is_paywall to the build_output_schema() properties so the schema matches serialized FetchResponse output.
• Extend the test_tool_schemas unit test to assert those three properties exist in the output schema.
• Minor formatting applied via cargo fmt as part of the change surface.

Testing

• Ran cargo fmt --all which completed successfully.
• Ran cargo test -p fetchkit test_tool_schemas and the test_tool_schemas assertion passed.

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Codex Task