Enforce mandatory issue linking in commit messages

[watermelon-admin]

Problem

Currently commit messages don't consistently reference issues, making it harder to track which changes relate to which requirements.

Solution

Update CLAUDE.md to make issue linking mandatory in all commit messages:

• Every commit MUST reference an issue using #123 format
• Every commit MUST include 'Closes #123', 'Fixes #123', or 'Resolves #123'
• Add clear examples of correct vs incorrect commit message formats
• Update GitHub Flow documentation to emphasize this requirement

Acceptance Criteria

• Update CLAUDE.md with mandatory commit message requirements
• Add commit message format examples
• Make requirements clearly visible with bold/emphasis formatting