chore: promote uat to production (Grype image vulnerability scanning)

Merges Grype-based container image vulnerability scanning and Docker CVE remediation to production.

- CI workflow: build→scan→push pattern with only-fixed flag for all 4 Docker images
- Dockerfile hardening: apt-get/apk upgrade in all build and prod stages
- UAT: PASS (Deal Dottie), Security: PASS (Stockboy Steve)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Dockerfile

@@ -1,4 +1,5 @@
 FROM node:22-alpine AS builder
+RUN apk update && apk upgrade --no-cache
 WORKDIR /app
 COPY package.json package-lock.json* ./
 RUN npm ci
@@ -7,6 +8,7 @@ COPY src/ src/
 RUN npm run build
 
 FROM node:22-alpine
+RUN apk update && apk upgrade --no-cache
 WORKDIR /app
 ENV NODE_ENV=production
 COPY package.json package-lock.json* ./

package-lock.json

@@ -941,9 +941,9 @@
       }
     },
     "node_modules/defu": {
-      "version": "6.1.4",
-      "resolved": "https://registry.npmjs.org/defu/-/defu-6.1.4.tgz",
-      "integrity": "sha512-mEQCMmwJu317oSz8CwdIOdwf3xMif1ttiM8LTufzc3g6kR+9Pe236twL8j3IYT1F7GfRgGcW6MWxzZjLIkuHIg==",
+      "version": "6.1.7",
+      "resolved": "https://registry.npmjs.org/defu/-/defu-6.1.7.tgz",
+      "integrity": "sha512-7z22QmUWiQ/2d0KkdYmANbRUVABpZ9SNYyH5vx6PZ+nE5bcC0l7uFvEfHlyld/HcGBFTL536ClDt3DEcSlEJAQ==",
       "license": "MIT"
     },
     "node_modules/delegates": {