fix(tui): bill Anthropic cache-write tokens at published rates (#4318)

[knqiufan]

Summary

• Keep Anthropic cache_creation_input_tokens as Usage::prompt_cache_write_tokens instead of folding them into cache-miss.
• Extend TUI CurrencyPricing with cache_write_per_million and publish 5-minute write rates for Anthropic/Qwen rows (e.g. claude-fable-5 at 12.50).
• Wire token_usage_for_pricing and turn-cost math so cache-write is no longer hardcoded to 0, fixing undercounted cost estimates.

Closes #4318

Testing

• cargo fmt --all -- --check (via cargo fmt -p codewhale-tui)
• cargo clippy --workspace --all-targets --all-features
• cargo test -p codewhale-tui --bin codewhale-tui --locked pricing::tests
• Anthropic usage mapping / SSE fixture / session_usage_cache_* / turn-metadata tests
• cargo test --workspace --all-features
• Spot-check a Claude turn with cache creation in the TUI cost estimate

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 (N/A — original authorship)

[github-actions]

Thanks @knqiufan for taking the time to contribute.

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