fix(skills): prevent PR description encoding corruption

[brianhdk]

Summary

• Update skill PR-body instructions to avoid encoding-related symbol corruption in GitHub-rendered PR descriptions.
• Replace interpolated here-string PR body generation with a safe template + Trello URL replacement pattern.
• Write PR body files explicitly as UTF-8 (Set-Content -Encoding utf8).

Scope

• SKILL instructions only (SKILL.md).
• No runtime application code, configs, or dependencies changed.

Validation

• Confirmed old @" ... | Set-Content C:\Users\mail\AppData\Local\Temp\pr-body-relewise-sdk-java.md pattern was removed.
• Confirmed TRELLO_CARD_URL templating and UTF-8 write instructions are present.