docs: sync translated READMEs (ko/ja/zh-CN) with Pydantic-first Quick Start

[yeongseon]

Priority: P2

Context

PR #290 (Closes #289) reworked the English README.md to lead with the clean Pydantic path:

• Quick Start now uses request_model= / response_model= with small BaseModel classes.
• Redundant route= / method= and @app.function_name(...) were dropped (the @openapi decorator infers route/method from the adjacent @app.route).
• Spec/Swagger UI plumbing (openapi.json / openapi.yaml / docs) moved into a collapsible <details> block.
• Raw JSON Schema path preserved in an "Advanced" <details> section.
• A note was added that @openapi documents the contract but does not validate (validation lives in azure-functions-validation).

The three translated READMEs still show the old pattern (@app.function_name, route=/method=, raw request_body dicts). As an interim measure, PR #290 added a "this translation may be outdated" banner to each. This issue tracks bringing them back in full parity.

Acceptance Checklist

• README.ko.md Quick Start / Before-After updated to match the English structure (Pydantic-first, folded plumbing, Advanced raw-schema <details>).
• README.ja.md updated to match.
• README.zh-CN.md updated to match.
• Add the "documents, not validates" note (localized) to each handler example.
• Remove the "outdated translation" banner from each file once it is synced.
• All Python code blocks parse (verify with ast.parse).

Out of scope

• Any further English README.md changes (handled in docs: lead README Quick Start with Pydantic models and drop redundant route/method #290 / docs: lead README Quick Start with Pydantic models and drop redundant route/method #289).
• Behavior/code changes.

References

• PR docs: lead README Quick Start with Pydantic models and drop redundant route/method #290 — English README rework.
• Issue docs: lead README Quick Start with Pydantic models and drop redundant route/method #289 — original English Quick Start improvement.
• src/azure_functions_openapi/decorator.py — _extract_binding_hints() route/method inference.