feat: add Docker deployment configuration

- Add multi-stage Dockerfile for static build
- Add nginx configuration with COOP/COEP headers for FFmpeg.wasm
- Add .dockerignore for optimized builds
- Enable SharedArrayBuffer support via security headers

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

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

.dockerignore

@@ -0,0 +1,44 @@
+# Dependencies
+node_modules
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+
+# Next.js
+.next
+out
+
+# Build
+dist
+build
+
+# Testing
+coverage
+
+# Env files
+.env*
+!.env.example
+
+# IDE
+.vscode
+.idea
+*.swp
+*.swo
+*~
+
+# Git
+.git
+.gitignore
+
+# Docker
+Dockerfile
+.dockerignore
+docker-compose.yml
+
+# Misc
+.DS_Store
+*.pem
+
+# Claude
+.claude