Fix changelog guidelines: PR format and automation reference

Fixes identified in code review:

1. PR link format: Changed from `[PR #123]` to `[PR 1818]` (no hash)
   - Analysis shows 165 entries without hash vs only 7 with hash
   - Aligns with actual project standard

2. Added reference to `bundle exec rake update_changelog`
   - This is the existing automation for updating version headers
   - Mentioned in CHANGELOG.md line 18 but was missing from guidelines

3. Verified file ends with newline (required per CLAUDE.md)

These changes ensure guidelines match actual usage and reference
existing automation tools.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

CLAUDE.md

@@ -48,10 +48,10 @@ Git hooks will automatically run linting on **all changed files (staged + unstag
 - **Do NOT add changelog entries for**: linting fixes, code formatting, internal refactoring, test updates, documentation fixes
 - Non-user-visible changes don't need changelog entries even if they modify code
 - **Format requirements**:
-  - Always link to the PR: `[PR #123](https://github.com/shakacode/react_on_rails/pull/123)`
+  - Always link to the PR: `[PR 1818](https://github.com/shakacode/react_on_rails/pull/1818)` (no hash symbol)
   - Always link to the author: `by [username](https://github.com/username)`
   - Keep formatting consistent with existing entries
-  - When releasing a version, update the version diff links at the bottom of CHANGELOG.md
+  - When releasing a version, run `bundle exec rake update_changelog` to update version headers and diff links
   - **For breaking changes**: Use bold formatting and link to migration documentation (e.g., `**Breaking**: Description. See [Migration Guide](docs/vX_upgrade.md)`)
 
 ## ⚠️ FORMATTING RULES