chore: add Claude Code configuration (#2)

## Summary
- Add `CLAUDE.md`: project description (K-pop shop backend, buffer in front of Hiboutik), architecture, domain notes, git workflow.
- Add shared `.claude/settings.json` (allowed dev commands, `.env` read protection).
- Pin the Prisma agent skills in `skills-lock.json` (restore with `npx skills experimental_install`, documented in the README).
- Update `.gitignore` (generated skills, local settings, Postman skills) and add `.gitattributes` (LF line endings).

## Note
This branch is based on `feat/customer-addresses-orders`, so the PR also contains the 3 feature commits (addresses, company details, orders) that `CLAUDE.md` describes.

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

Co-authored-by: MastersGame <quentin.duwa1210@gmail.com>
Reviewed-on: #2

README.md

@@ -31,6 +31,14 @@
 $ npm install
 ```
 
+### AI agent skills (optional)
+
+The Prisma skills used by Claude Code are pinned in `skills-lock.json`; the skill folders themselves are not committed. Restore them with:
+
+```bash
+$ npx skills experimental_install
+```
+
 ## Compile and run the project
 
 ```bash