fix(supported-languages): pull write writing_style and tone languages automatically from vended v3/languages response

[daniel-jones-dev]

Summary

Switches the writing_style and tone ParamFields in api-reference/improve-text.mdx from the hardcoded bullet lists back to <SupportedLanguages mode="bullets" resource="write" feature="..." direction="target" />, so both lists derive automatically from the vended /v3/languages?resource=write response.

Blocked until the write response is correct. The vended write.json currently only flags writing_style / tone on de, en-GB, en-US. The hardcoded list ships 8 languages (also es, fr, it, pt-BR, pt-PT). Merge this only after the API team has fixed the /v3/languages?resource=write response so the rendered list matches reality.

Stacked on #355.

Test plan

• Once the API is fixed and data/v3-languages/write.json is refreshed, render mint dev → /api-reference/improve-text and confirm both writing_style and tone ParamFields list the expected target languages.
• Compare against the previously hardcoded list (de, en-GB, en-US, es, fr, it, pt-BR, pt-PT); flag any mismatch with the API team before merging.

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