fix(security #17): add npm audit to CI pipeline and package scripts

Added .gitea/workflows/ci.yml which runs 'npm audit --audit-level=moderate'
on every push and PR. Fails the build on any moderate or higher severity
finding.

Also added 'npm run audit' and 'npm run audit:fix' convenience scripts
to package.json for local use.

package.json

@@ -6,7 +6,9 @@
   "scripts": {
     "dev": "nodemon server/index.js",
     "start": "node server/index.js",
-    "install:all": "npm install"
+    "install:all": "npm install",
+    "audit": "npm audit --audit-level=moderate",
+    "audit:fix": "npm audit fix"
   },
   "dependencies": {
     "axios": "^1.6.0",