fix: align app/db image bases with documented stack (E00-S02-T01)

Switch the app image from node:24-alpine to node:24.19.0-bookworm-slim in
both build and runtime stages (Technology-Stack 5.4: glibc Debian base
required because argon2 is a native dependency; musl/Alpine causes
native-module build surprises), and the db image from postgres:16-alpine
to postgres:18-bookworm (Technology-Stack 5.2/5.4/6.2 + golden tuple 7
pin PostgreSQL 18.6; 18-bookworm is the 18.x line on Debian bookworm).

Update tests/compose-config.test.mjs so the committed assertions lock in
the corrected image bases (db image, Dockerfile build/runtime stages,
parser probe).

apps/server/Dockerfile

@@ -3,15 +3,19 @@
 # @personal-blog/server — EPPP public server application image.
 #
 # [E00-S02-T01] baseline: builds the workspace server package with the pinned
-# toolchain (Node 24 + pnpm 11.23.0, frozen lockfile) and runs the compiled
+# toolchain (Node 24.19.0 + pnpm 11.23.0, frozen lockfile) and runs the compiled
 # entrypoint. The server is still a bootstrap placeholder (its module loads and
 # exits cleanly); the Fastify 5 application shell that turns it into a serving
 # process lands in a later story, and the health gate (T02), health endpoint
 # (T03), volume persistence (T04), non-root/read-only hardening and multi-arch
 # targets are later E00-S02 tasks — all out of scope here.
+#
+# Image base: node:24.19.0-bookworm-slim (glibc Debian) per Technology-Stack
+# §5.4 — argon2 is a native dependency and musl/Alpine causes native-module
+# build surprises, so the image must stay on a glibc base.
 
 # --- build stage: install the frozen workspace and compile the server --------
-FROM node:24-alpine AS build
+FROM node:24.19.0-bookworm-slim AS build
 WORKDIR /app
 
 # Enable the pinned pnpm (11.23.0, via packageManager in the root package.json)
@@ -33,8 +37,8 @@ RUN pnpm install --frozen-lockfile
 COPY apps/server apps/server
 RUN pnpm --filter @personal-blog/server build
 
-# --- runtime stage: Node 24 + compiled output only ----------------------------
-FROM node:24-alpine AS runtime
+# --- runtime stage: Node 24.19.0 (bookworm-slim) + compiled output only ------
+FROM node:24.19.0-bookworm-slim AS runtime
 WORKDIR /app
 ENV NODE_ENV=production