feat: initial FitCoach Pro lead management app

Next.js 16 app with full CRUD lead management:
- REST API (/api/leads) with GET (pagination), POST, PUT, DELETE (soft delete)
- Zod validation (server + client), Supabase (PostgreSQL)
- Responsive UI: leads table (desktop) + cards (mobile), modal form, toast notifications
- 43 tests (Vitest + React Testing Library): validation, components, pagination
- Docker setup (multi-stage build, health check)
- Supabase migration + 15 seed leads
- Documentation (CLAUDE.md, README, API docs)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,68 @@
+# Dependencies
+/node_modules
+/.pnp
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/versions
+
+# Testing
+/coverage
+
+# Next.js
+/.next/
+/out/
+
+# Production
+/build
+
+# Secrets & Credentials (NIEMALS COMMITTEN!)
+.env
+.env.*
+!.env.example
+*.pem
+*.key
+*.p12
+*.pfx
+credentials.json
+secrets.json
+service-account*.json
+
+# temp/ - Lokale Entwicklungsnotizen
+temp/
+tmp/
+*.tmp
+*.bak
+*.swp
+*.swo
+*~
+
+# Claude Code
+.claude/commands/
+.claude/settings.local.json
+.claude/worktrees/
+
+# Debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# OS
+.DS_Store
+Thumbs.db
+
+# IDE
+.idea/
+.vscode/
+*.sublime-*
+*.code-workspace
+
+# TypeScript
+*.tsbuildinfo
+next-env.d.ts
+
+# Vercel
+.vercel