R2: drop ./loadtest from the backend/gateway/telegram image builds

Adding the loadtest module to go.work (use ./loadtest + the scrabble/gateway
replace it needs) broke the other services' Docker builds: their reduced
workspace still referenced ./loadtest (not in their build context), failing with
'cannot load module loadtest: open loadtest/go.mod: no such file or directory'.
Each service Dockerfile now also -dropuse=./loadtest; backend and telegram (which
do not COPY ./gateway) additionally -dropreplace the loadtest-only scrabble/gateway
replace. Verified by building all three images plus loadtest locally.

backend/Dockerfile

@@ -30,8 +30,9 @@ COPY go.work go.work.sum ./
 COPY pkg ./pkg
 COPY backend ./backend
 
-# Reduce the workspace to what the backend needs: backend + pkg.
+# Reduce the workspace to what the backend needs: backend + pkg. loadtest and the
-RUN go work edit -dropuse=./gateway -dropuse=./platform/telegram
+# gateway replace it requires are not in this context, so drop both.
+RUN go work edit -dropuse=./gateway -dropuse=./platform/telegram -dropuse=./loadtest -dropreplace=scrabble/gateway@v0.0.0
 RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -o /out/backend ./backend/cmd/backend
 
 # --- runtime -----------------------------------------------------------------

gateway/Dockerfile

@@ -50,8 +50,9 @@ COPY gateway ./gateway
 RUN rm -rf gateway/internal/webui/dist
 COPY --from=ui /ui/dist gateway/internal/webui/dist
 
-# Reduce the workspace to what the gateway needs: gateway + pkg.
+# Reduce the workspace to what the gateway needs: gateway + pkg (loadtest is not in
-RUN go work edit -dropuse=./backend -dropuse=./platform/telegram
+# this context; its scrabble/gateway replace targets ./gateway, which is present here).
+RUN go work edit -dropuse=./backend -dropuse=./platform/telegram -dropuse=./loadtest
 RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -o /out/gateway ./gateway/cmd/gateway
 
 # --- runtime -----------------------------------------------------------------

platform/telegram/Dockerfile

@@ -1,8 +1,9 @@
 # Telegram connector image.
 #
 # The connector imports only the shared scrabble/pkg module, so the build drops the
-# other workspace modules (backend, gateway) and the scrabble-solver replace from a
+# other workspace modules (backend, gateway, loadtest), the loadtest-only
-# copy of go.work: it needs neither their sources nor the solver sibling checkout.
+# scrabble/gateway replace and the scrabble-solver replace from a copy of go.work: it
+# needs neither their sources nor the solver sibling checkout.
 # Build from the repository ROOT so go.work, pkg/ and platform/telegram/ are all in
 # the context (see deploy/docker-compose.yml, which sets context: ../../..).
 FROM golang:1.26.3-alpine AS build
@@ -13,7 +14,7 @@ COPY pkg ./pkg
 COPY platform/telegram ./platform/telegram
 
 # Reduce the workspace to what the connector needs: only pkg + platform/telegram.
-RUN go work edit -dropuse=./backend -dropuse=./gateway -dropreplace=scrabble-solver
+RUN go work edit -dropuse=./backend -dropuse=./gateway -dropuse=./loadtest -dropreplace=scrabble/gateway@v0.0.0 -dropreplace=scrabble-solver
 
 RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -o /out/telegram ./platform/telegram/cmd/telegram