docs(github): move PR template to GitHub idiomatic location

[KemingHe]

CHANGES

• Move PR template from PULL_REQUEST_TEMPLATE/ to root .github/
• Update commit message prompt with multi-issue linking format
• Update PR generation prompt with issue linking guidelines

IMPACT

• GitHub will automatically detect PR template in standard location
• Improved AI prompt consistency with KemingHe/common-devx standards

[Copilot]

Pull Request Overview

This PR standardizes the repository's GitHub workflows by moving the PR template to GitHub's expected location and updating AI prompts to support proper multi-issue linking format.

• Move PR template from non-standard PULL_REQUEST_TEMPLATE/ directory to standard .github/ location
• Update commit message and PR generation prompts to clarify multi-issue linking guidelines

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
prompts/prompt-pull-request-gen.md	Added guidance for separate "closes #[issue-number]" statements per resolved issue
prompts/prompt-commit-msg-gen.md	Updated issue linking format to support multiple issues with separate "closes" statements

Comments suppressed due to low confidence (1)

prompts/prompt-commit-msg-gen.md:58

• There's an extra dash in the bullet point. It should be "- Issue linking" not "-- Issue linking".

- **Content**: Only include sections with meaningful content, use dash bullets with no redundancy between items

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