feat: update prompt

[earayu]

Note

Strengthens search scoping and clarifies responses across prompts.

• Enforces restriction to search ONLY user-@Specified collections; fall back to autonomous discovery only when none are specified (English and Chinese system and default query templates)
• Simplifies/clarifies citation guidance and sources section (single - [Collection Name]: [Key findings] format; always use collection names, not IDs)
• Adjusts research instructions ordering/wording; keeps web search usage explicit and language consistency intact
• No functional code changes beyond prompt/template text updates in aperag/service/prompt_template_service.py

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