chore: add Claude Code configuration

- add CLAUDE.md (project description, architecture, domain notes, git workflow)
- add shared .claude/settings.json (allowed commands, .env read protection)
- pin Prisma agent skills in skills-lock.json and document how to restore them
- ignore generated skills, local settings and Postman skills in .gitignore
- add .gitattributes to normalize line endings to LF

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.claude/settings.json

@@ -0,0 +1,17 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(npm run lint)",
+      "Bash(npm run build)",
+      "Bash(npm test)",
+      "Bash(npm run test:e2e)",
+      "Bash(npx jest:*)",
+      "Bash(npx prisma generate --config prisma7.config.ts)"
+    ],
+    "deny": [
+      "Read(./.env)",
+      "Read(./.env.*)",
+      "Bash(cat .env*)"
+    ]
+  }
+}