docs: sync translated READMEs with Pydantic-first Quick Start

[yeongseon]

Summary

Brings the ko/ja/zh-CN READMEs back into parity with the English Pydantic-first Quick Start (reworked in #290 / #289).

• Before / After: adds the localized section that leads with request_model= / response_model= Pydantic models.
• Quick Start: reworked to the clean Pydantic path; @openapi infers route/method from @app.route, and the openapi.json / openapi.yaml / docs plumbing is folded into a <details> block.
• Advanced: raw JSON Schema path preserved under an "Advanced" <details> section.
• Adds the localized "documents the contract but does not validate (validation lives in azure-functions-validation)" note to each handler.
• Removes the "this translation may be outdated" banner from all three files.

Verification

• All Python code blocks in every README parse via ast.parse (5 blocks each, matching the English README).

Closes #291

[Copilot]

Pull request overview

This PR updates the Korean, Japanese, and Simplified Chinese READMEs to match the current English “Pydantic-first” Quick Start structure, keeping the localized docs aligned with the recommended usage patterns for azure-functions-openapi.

Changes:

• Adds localized Before / After sections demonstrating the Pydantic request_model= / response_model= workflow.
• Reworks Quick Start examples to rely on @openapi route/method inference from @app.route, and folds spec/Swagger UI wiring into a <details> block.
• Preserves the raw JSON Schema approach under an Advanced <details> section and adds the localized “documents, not validates” note.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
README.ko.md	Syncs Korean README to the English Pydantic-first Quick Start structure, including details blocks and advanced raw-schema example.
README.ja.md	Syncs Japanese README to the English Pydantic-first Quick Start structure, including details blocks and advanced raw-schema example.
README.zh-CN.md	Syncs Simplified Chinese README to the English Pydantic-first Quick Start structure, including details blocks and advanced raw-schema example.