[ci skip] Move Terraform modules into stack directories

Move all 88 service modules (66 individual + 22 platform) from
modules/kubernetes/<service>/ into their corresponding stack directories:

- Service stacks: stacks/<service>/module/
- Platform stack: stacks/platform/modules/<service>/

This collocates module source code with its Terragrunt definition.
Only shared utility modules remain in modules/kubernetes/:
ingress_factory, setup_tls_secret, dockerhub_secret, oauth-proxy.

All cross-references to shared modules updated to use correct
relative paths. Verified with terragrunt run --all -- plan:
0 adds, 0 destroys across all 68 stacks.

stacks/platform/modules/k8s-portal/files/Dockerfile

@@ -0,0 +1,15 @@
+FROM node:22-alpine AS build
+WORKDIR /app
+COPY package*.json ./
+RUN npm ci
+COPY . .
+RUN npm run build
+
+FROM node:22-alpine
+WORKDIR /app
+COPY --from=build /app/build ./build
+COPY --from=build /app/package.json ./
+COPY --from=build /app/node_modules ./node_modules
+ENV PORT=3000
+EXPOSE 3000
+CMD ["node", "build"]