Docs: Align changelog with new feature rollouts (e.g., slash command positional arguments)

Title: Docs: Align changelog with new feature rollouts (e.g., slash command positional arguments)

Body:

Hi Claude Code team,

It appears there might be a delay between when new features are documented and when they appear in the official CHANGELOG.md. This can make it challenging for users who follow the changelog to discover and adopt new capabilities as they are released.

A specific example is the recent introduction of positional arguments ($1, $2, etc.) for custom slash commands. This is a fantastic enhancement that allows for much more powerful and structured commands.

The feature is now live in the official documentation under the "Slash commands" page:

#### Arguments Pass dynamic values to commands using argument placeholders: ##### All arguments with $ARGUMENTS The $ARGUMENTS placeholder captures all arguments passed to the command... ##### Individual arguments with $1, $2, etc. Access specific arguments individually using positional parameters (similar to shell scripts): ``bash # Command definition echo 'Review PR #$1 with priority $2 and assign to $3' > .claude/commands/review-pr.md # Usage > /review-pr 456 high alice # $1 becomes "456", $2 becomes "high", $3 becomes "alice" ``

However, after reviewing the CHANGELOG.md, this new functionality doesn't seem to be mentioned in any of the recent versions.

Many developers rely on the changelog to stay informed about new features, understand the evolution of the tool, and decide when to update. When valuable improvements like this are missed, it can hinder adoption and user awareness.

Request:

Could you please ensure that the official changelog is updated in tandem with feature releases and documentation updates? Keeping these resources aligned would greatly improve the developer experience for everyone following the project.

Thank you