[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/excalidraw/module/project/Dockerfile

@@ -0,0 +1,22 @@
+FROM golang:1.21-alpine AS builder
+
+WORKDIR /app
+COPY go.mod ./
+COPY main.go ./
+COPY static/ ./static/
+
+RUN go build -o excalidraw-library .
+
+FROM alpine:latest
+
+RUN apk --no-cache add ca-certificates
+
+WORKDIR /app
+COPY --from=builder /app/excalidraw-library .
+
+ENV DATA_DIR=/data
+ENV PORT=8080
+
+EXPOSE 8080
+
+CMD ["./excalidraw-library"]