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>

package.json

@@ -1,8 +1,11 @@
 {
   "name": "n8n-mcp",
-  "version": "2.7.6",
+  "version": "2.7.8",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
+  "bin": {
+    "n8n-mcp": "./dist/mcp/index.js"
+  },
   "scripts": {
     "build": "tsc",
     "rebuild": "node dist/scripts/rebuild.js",
@@ -42,7 +45,8 @@
     "db:rebuild": "node dist/scripts/rebuild-database.js",
     "db:init": "node -e \"new (require('./dist/services/sqlite-storage-service').SQLiteStorageService)(); console.log('Database initialized')\"",
     "docs:rebuild": "ts-node src/scripts/rebuild-database.ts",
-    "sync:runtime-version": "node scripts/sync-runtime-version.js"
+    "sync:runtime-version": "node scripts/sync-runtime-version.js",
+    "prepare:publish": "./scripts/publish-npm.sh"
   },
   "repository": {
     "type": "git",
@@ -62,6 +66,14 @@
     "url": "https://github.com/czlonkowski/n8n-mcp/issues"
   },
   "homepage": "https://github.com/czlonkowski/n8n-mcp#readme",
+  "files": [
+    "dist/**/*",
+    "data/nodes.db",
+    ".env.example",
+    "README.md",
+    "LICENSE",
+    "package.runtime.json"
+  ],
   "devDependencies": {
     "@types/express": "^5.0.3",
     "@types/jest": "^29.5.14",