feat: add npx support for zero-installation usage (closes #15)

- Add bin configuration to package.json for npx execution
- Implement smart database path resolution for npx/global/local installs
- Create dedicated npm publish script using runtime-only dependencies
- Add .npmignore to control published package contents
- Update README with npx as primary installation method
- Add n8n version badge to README
- Sync version between package.json and package.runtime.json
- Update CHANGELOG for v2.7.8 release

This allows users to run 'npx n8n-mcp' without installing the package,
reducing friction and making it easier to get started with n8n-MCP.

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

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

.npmignore

@@ -0,0 +1,72 @@
+# Source files (TypeScript)
+src/
+*.ts
+!dist/**/*.d.ts
+
+# Development files
+.github/
+scripts/
+tests/
+docs/
+*.test.js
+*.spec.js
+
+# Build files
+tsconfig.json
+jest.config.js
+nodemon.json
+renovate.json
+
+# Docker files (not needed for npm)
+Dockerfile*
+docker-compose*.yml
+docker/
+.dockerignore
+
+# Environment and config files
+.env
+.env.*
+!.env.example
+
+# IDE and OS files
+.vscode/
+.idea/
+*.swp
+.DS_Store
+
+# Logs and temp files
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+*.pid
+*.seed
+*.pid.lock
+
+# Coverage and test reports
+coverage/
+.nyc_output/
+
+# Git files
+.git/
+.gitignore
+
+# Documentation source files
+*.md
+!README.md
+!LICENSE
+
+# Package files we don't want to publish
+package-lock.json
+yarn.lock
+pnpm-lock.yaml
+
+# Backup files
+*.backup
+*.bak
+
+# Keep only necessary runtime files
+!dist/
+!data/nodes.db
+!package.json
+!package.runtime.json