fix(docker): install python3/make/g++ toolchain for re2 native build

The develop image build broke at `pnpm install --frozen-lockfile`: the new
native dependency re2@1.25.0 (packages/mcp, search_in_page #330) always
compiles from source under pnpm — its prebuilt-binary downloader
(install-artifact-from-github) cannot identify the GitHub repo because pnpm
does not populate npm_package_repository_*/npm_package_json env vars ("No
github repository was identified. Building locally ..."), and node:22-slim
ships no python3/make/g++ for the node-gyp fallback.

- builder stage: add a cache-friendly apt layer with python3 make g++
  before COPY; the stage is discarded so the toolchain may stay.
- installer stage: install the toolchain, run the prod install as the node
  user via `su node -c`, and purge the toolchain — all in one RUN layer so
  the final image stays slim and node_modules ownership needs no extra
  chown layer; USER node is restored right after.

Fixes the failed run 28715009124 (develop docker build); release.yml uses
the same Dockerfile and is covered too.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Dockerfile

@@ -5,6 +5,13 @@ RUN npm install -g pnpm@10.4.0
 
 FROM base AS builder
 
+# re2 (packages/mcp) always compiles from source under pnpm (the prebuilt-binary
+# download cannot identify the GitHub repo), so node-gyp needs python3/make/g++.
+# This stage is discarded, so the toolchain can stay installed.
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends python3 make g++ \
+  && rm -rf /var/lib/apt/lists/*
+
 WORKDIR /app
 
 COPY . .
@@ -57,9 +64,16 @@ COPY --from=builder /app/patches /app/patches
 
 RUN chown -R node:node /app
 
-USER node
+# Toolchain is needed transiently to compile re2 during the prod install; install
+# and purge it in one layer to keep the final image slim. The install itself runs
+# as the node user via su to keep node_modules ownership without a costly chown layer.
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends python3 make g++ \
+  && su node -c "pnpm install --frozen-lockfile --prod" \
+  && apt-get purge -y --auto-remove python3 make g++ \
+  && rm -rf /var/lib/apt/lists/*
 
-RUN pnpm install --frozen-lockfile --prod
+USER node
 
 RUN mkdir -p /app/data/storage