docs: add README.md, update .gitignore, include design and implementation docs

.gitignore

@@ -1,8 +1,38 @@
+# Dependencies
 node_modules/
+
+# Build output
 dist/
+
+# Environment
 .env
+.env.local
+.env.*.local
+
+# Logs
 *.log
+npm-debug.log*
+pnpm-debug.log*
+
+# OS
 .DS_Store
+Thumbs.db
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
 
 # Docker
 docker-compose.override.yml
+
+# Claude Code
+.claude/
+
+# Prisma
+prisma/*.db
+prisma/*.db-journal
+
+# Test coverage
+coverage/