feat: bootstrap b2bcall saas architecture

- monorepo skeleton (apps/, packages/, infrastructure/, scripts/, docs/)
- docker-compose with PostgreSQL 18 and Redis 7 (localhost-only)
- .gitignore and .env.example
- initial TODO.md and docs/ARCHITECTURE.md

.gitignore

@@ -0,0 +1,32 @@
+# Secrets — never commit
+.env
+.env.*
+!.env.example
+FIRST_LOGIN.txt
+*.pem
+*.key
+
+# Dependencies
+node_modules/
+.pnpm-store/
+
+# Build output
+dist/
+build/
+.next/
+.turbo/
+
+# Logs
+*.log
+npm-debug.log*
+
+# OS
+.DS_Store
+Thumbs.db
+
+# IDE
+.vscode/
+.idea/
+
+# Docker volumes / data
+infrastructure/**/data/