🧹 remove duplicate _apply_prefix and _determine_ruri_prefix functions

[chottokun]

🎯 What: Removed duplicate implementations of _apply_prefix and _determine_ruri_prefix in src/app/main.py by re-exporting them from src/app/services/embedding.py.

💡 Why: Having duplicate helper function implementations in main.py and services/embedding.py increased maintenance overhead and potential risk of logic divergence. Re-exporting from the canonical implementation in services/embedding.py maintains backwards compatibility for unit tests while eliminating duplicate code.

✅ Verification:

• Ran uv run ruff check src/ and uv run ruff format --check src/ to confirm code style and lint compliance.
• Executed the full test suite with uv run pytest, verifying that all 149 unit and integration tests passed.

✨ Result: Reduced code duplication in src/app/main.py and consolidated prefix handling logic into src/app/services/embedding.py.

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PR created automatically by Jules for task 320161055953050528 started by @chottokun

[google-labs-jules]

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[chottokun]

本PRのリファクタリング内容（プレフィックス重複排除）は、モデル共通化リファクタリングを統合した PR #88 にて包括的にブラッシュアップを進めています。PR #88 のマージ完了後に本PRをクローズ予定です。

[google-labs-jules]

本PRのリファクタリング内容（プレフィックス重複排除）は、モデル共通化リファクタリングを統合した PR #88 にて包括的にブラッシュアップを進めています。PR #88 のマージ完了後に本PRをクローズ予定です。

ご共有いただきありがとうございます。PR #88 でのモデル共通化リファクタリングへの統合および本PRのクローズ予定について承知いたしました。