docs: clarify log message capitalization guidance

[kvinwang]

Summary

• clarify that log and error messages generally start with lowercase text
• preserve conventional capitalization for leading identifiers and acronyms
• add a RIM example to make the exception explicit

Testing

• Documentation-only change

[Copilot]

Pull request overview

This PR updates the repository’s contributor guidance (CLAUDE.md) to more precisely describe how to capitalize log and error messages, including an explicit exception for leading acronyms/identifiers (e.g., RIM).

Changes:

• Reword the rule to “start with lowercase” rather than “never capitalize”.
• Clarify the exception for leading identifiers/acronyms and add an explicit RIM example.
• Remove the statement about enforcement in .cursorrules from this section.

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