fix(build): unify Go version to 1.24 across Dockerfile and CI

SEC-09: go.mod declares Go 1.24.0 but Dockerfile.production used 1.23
and backend-ci.yml used 1.23. Aligned both to 1.24.

.github/workflows/backend-ci.yml

@@ -24,7 +24,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.23"
+          go-version: "1.24"
           cache: true
 
       - name: Download deps
@@ -87,7 +87,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.23"
+          go-version: "1.24"
           cache: true
 
       - name: Download deps

veza-backend-api/Dockerfile.production

@@ -2,7 +2,7 @@
 # Optimized for smaller size and security
 
 # Build stage
-FROM golang:1.23-alpine AS builder
+FROM golang:1.24-alpine AS builder
 
 WORKDIR /app