build(docker): move image to node 24 and install pnpm without corepack

Supersedes #1250. Dependabot's 22 -> 26 bump fails the image build with
`corepack enable` exiting 127: Node 25 unbundled Corepack, so it is simply not
in the base image any more.

Two changes instead:

- both stages move to `node:24-alpine`, the current LTS line. Node 26 is still
  Current until October 2026, so it is the wrong target for a self-hosted
  runtime image.
- pnpm is installed globally at the exact `packageManager` version instead of
  through Corepack, which keeps the install reproducible and stops the next
  base-image major from breaking the build the same way.

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

docker/Dockerfile

@@ -1,7 +1,7 @@
 # The Nx builds below emit platform-independent JS/static assets. During
 # multi-arch publish builds, keep that heavy build stage on the native builder
 # platform instead of running Node/Nx through QEMU for linux/arm64.
-FROM --platform=$BUILDPLATFORM node:22-alpine AS build
+FROM --platform=$BUILDPLATFORM node:24-alpine AS build
 
 RUN apk add --no-cache python3 make g++ git
 
@@ -11,7 +11,12 @@ COPY .npmrc ./
 COPY package.json pnpm-lock.yaml ./
 COPY patches ./patches
 
-RUN corepack enable && pnpm install --frozen-lockfile --ignore-scripts
+# Node 25 unbundled Corepack, so `corepack enable` cannot be the way pnpm gets
+# installed here — it would break on the next base-image major. Install the
+# exact pnpm from `packageManager` instead, which stays reproducible.
+RUN PNPM_VERSION="$(node -p 'require("./package.json").packageManager.split("@")[1].split("+")[0]')" \
+    && npm install --global "pnpm@${PNPM_VERSION}" \
+    && pnpm install --frozen-lockfile --ignore-scripts
 
 COPY . .
 
@@ -23,7 +28,7 @@ RUN node tools/build/inject-build-commit.mjs
 RUN pnpm nx build web --configuration=pwa
 RUN pnpm nx build web-backend
 
-FROM node:22-alpine
+FROM node:24-alpine
 
 RUN apk add --no-cache gettext nginx
 

docs/architecture/pwa-self-hosted.md

@@ -175,7 +175,10 @@ browser sidecar data.
 The Docker image has two stages:
 
 1. Build stage installs dependencies and runs `web:pwa` plus `web-backend`.
-2. Runtime stage uses `node:22-alpine` with nginx installed. nginx serves
+   pnpm is installed globally at the exact `packageManager` version rather than
+   through Corepack, which Node 25 unbundled, so the base-image major stays
+   free to move.
+2. Runtime stage uses `node:24-alpine` with nginx installed. nginx serves
    `dist/apps/web` and proxies `/api/*` to the local Express backend.
    The entrypoint renders the nginx config from a `${PORT}` template, starts the
    backend, waits for `/health`, and then starts nginx. If either process exits