fix(web): display slash command args in message view

[DrumRobot]

Summary

• Display commandData.args alongside the command name in slash command messages
• Previously only the command name was shown (e.g., /session), now args are also displayed (e.g., /session repair --dry-run)
• Add Storybook stories for MessageItem slash command rendering

Relates to #53

Test plan

• Verify slash commands with args display correctly in web session viewer
• Verify slash commands without args still display correctly
• Verify component in Storybook (MessageItem stories)
• Build passes
• All existing tests pass

[Copilot]

Pull request overview

Fixes the web session viewer’s slash command rendering so that command arguments (commandData.args) are displayed alongside the command name, aligning behavior with existing command title rendering and the expected UX from #53.

Changes:

• Render commandData.args next to the slash command name in MessageItem.svelte.
• Add Storybook stories covering slash command rendering with and without args.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/web/src/lib/components/MessageItem.svelte	Updates slash command message header to conditionally render parsed command args.
packages/web/src/lib/components/MessageItem.stories.svelte	Adds Storybook coverage for slash command messages with/without args.

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[Copilot]

In this flex justify-between header, adding args as a separate sibling creates 3 flex children, so justify-between will push the args toward the middle instead of keeping it adjacent to the command name. Consider grouping the command name + args into a single left-side container (e.g., a nested div/span with flex items-center gap-1 min-w-0), and optionally add truncate/overflow-hidden so long args don’t shove the timestamp/buttons off-screen.

Suggested change

	<span class="font-semibold text-gh-accent">{commandData.name || 'Command'}</span>
	{#if commandData.args}
	<span class="text-gh-text-secondary ml-1">{commandData.args}</span>
	{/if}
	<div class="flex items-center gap-2">
	<div class="flex items-center gap-1 min-w-0">
	<span class="font-semibold text-gh-accent">{commandData.name || 'Command'}</span>
	{#if commandData.args}
	<span class="text-gh-text-secondary truncate">{commandData.args}</span>
	{/if}
	</div>
	<div class="flex items-center gap-2 flex-shrink-0">