feat(AdminSidebar): add sidebar component with Storybook stories

[krmlp]

📄 Summary

This PR introduces the AdminSidebar component for the admin/layout module.

The component is implemented in Pioneer Strict Mode, serving as a reference sidebar that enforces the project's highest architectural standards: explicit configuration, composition-first design, and full i18n/a11y compliance.

• Strict configuration: No default values. All visual and behavioral options (variants, sizes, widths, badge variants) are required props.
• No embedded strings: All user-facing and assistive text (ariaLabel, expandAriaLabel, collapseAriaLabel) is passed explicitly for i18n.
• Core components only: Built using Button, Link, Badge, Heading, Text, Spinner, and Icon.
• Collapsible submenu pattern: Uses native details/summary for nested menus (DaisyUI standard pattern).
• Composition-first design: Header, footer, and children content are injected via snippets to avoid layout-level coupling.
• Svelte 5 runes: Uses $props, $derived, and $bindable.

🧩 Affected Module(s)

• Source Code
• Documentation
• CI / Infra

✏️ PR Title Format

✅ PR Title: feat(AdminSidebar): add sidebar component with Storybook stories

✅ Checklist

• My branch name follows format: feat/admin-sidebar
• My PR title starts with one of the approved types listed above
• My code is formatted using Prettier (pnpm format)
• I ran static analysis (pnpm check) and resolved warnings
• I linked related issues using keywords like Closes #217
• I ensured this PR has no unrelated changes
• This PR is ready for review and does not include unfinished work

🔗 Related Issues

Closes #217

[husamettinarabaci]

LGTM