feat: implement optimization #5 - CHANGELOG section generation

Add automated CHANGELOG section preparation for releases:

- Create ChangelogEditor class for programmatic CHANGELOG.md editing
- Implement create_version_section() to create new release sections
- Automatically move [Unreleased] content to new version section
- Add 'release prepare VERSION' CLI command to prepare CHANGELOG
- Validate CHANGELOG after edit to ensure correctness
- Support custom release dates with --date option
- Provide helpful feedback about content movement

This streamlines release preparation by automating the manual task of
creating version sections and moving unreleased changes.

Usage:
  release prepare 0.11.0            # Uses today's date
  release prepare 0.11.0 --date 2026-01-15

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

capabilities/release-management/src/release_management/cli/main.py

@@ -11,6 +11,7 @@ from typing import Optional
 
 from ..core.manager import ReleaseManager
 from ..utils.version import VersionManager
+from ..changelog.editor import ChangelogEditor
 
 
 @click.group(invoke_without_command=True)
@@ -286,5 +287,44 @@ def check_consistency(ctx, version: str):
         sys.exit(1)
 
 
+@main.command('prepare')
+@click.argument('version')
+@click.option('--date', default=None, help='Release date (YYYY-MM-DD, defaults to today)')
+@click.pass_context
+def prepare(ctx, version: str, date: Optional[str]):
+    """Prepare CHANGELOG for new version release.
+
+    Creates a new version section in CHANGELOG.md and moves all content
+    from the [Unreleased] section to the new version section.
+    """
+    project_root = ctx.obj['project_root'] or Path.cwd()
+    changelog_path = project_root / 'CHANGELOG.md'
+
+    editor = ChangelogEditor(changelog_path)
+
+    # Create version section
+    if editor.create_version_section(version, date):
+        # Validate result
+        manager = ReleaseManager(
+            project_root=ctx.obj['project_root'],
+            dry_run=ctx.obj['dry_run'],
+            force=ctx.obj['force']
+        )
+
+        # Check if CHANGELOG is valid after edit
+        is_valid, issues = manager.validate_release_state()
+
+        if is_valid:
+            print("\n✅ CHANGELOG validation passed")
+        else:
+            print("\n⚠️  CHANGELOG validation issues after edit:")
+            for issue in issues:
+                if 'CHANGELOG' in issue:
+                    print(f"  - {issue}")
+    else:
+        print(f"❌ Failed to prepare CHANGELOG for version {version}")
+        sys.exit(1)
+
+
 if __name__ == '__main__':
     main()