Claude Code: Add Claude Code rules, commands, and authoring skill

Is your feature request related to a problem?
AI-assisted contributions to kaapi-frontend currently have no codified conventions — each session re-derives component structure, hook patterns, API proxy style, and quality limits from scratch, producing inconsistent code and repeated review feedback. There is also no standard workflow for verification, issue creation, or PR drafting.

Describe the solution you'd like
Add a .claude/ toolset that encodes the repo's conventions and workflows:

• Rules (.claude/rules/): seven auto-loaded convention files — components.md, hooks.md, api-and-data-fetching.md, styling.md, types-and-constants.md, utils.md, code-quality.md (500 LOC limit, complexity caps, file-splitting seams).
• new-feature skill (.claude/skills/new-feature/SKILL.md): 7-step authoring contract — branch, orient via rules, reuse-first scan, correct placement, in-style writing, limits, lint+build verification.
• Commands (.claude/commands/): /check (drive lint + production build to green), /create-issue (templated feature/enhancement issues), /create-pr (Issue link + Summary PR format), plus a pr-review update.