fix(docker): use pnpm deploy for self-contained gateway image

Root cause: the runner stage copied /app/node_modules (the pnpm
content-addressed .pnpm store) instead of apps/gateway/node_modules
(which holds the symlinks Node.js uses to resolve packages relative
to the gateway entrypoint). In a stripped image without pnpm's virtual
store topology, dotenv and every other dep were unresolvable, causing
ERR_MODULE_NOT_FOUND on startup.

Fix: replace the broken node_modules copy with `pnpm deploy --legacy`
which produces a flat, self-contained node_modules at /deploy — no
workspace symlinks required. Also corrected the filter name (@mosaic/gateway
→ @mosaicstack/gateway), added COPY plugins/ to the pre-install step so
turbo's dependency graph can resolve the telegram/discord plugins that
are workspace deps of the gateway, and switched the build step to
`pnpm turbo run build --filter @mosaicstack/gateway...` so all
transitive workspace packages are compiled in topological order before
the gateway.

Verification: local build succeeded (image sha256:dd44b49b5cf49bafd91f8733792b25b08a4711d2ee1bb278460aea747c305bd0,
~254 MB). Running the image with stub env reaches Postgres connection
error (TierDetectionError: postgres unreachable at nope:5432) — dotenv
loads cleanly, past module resolution. No ERR_MODULE_NOT_FOUND.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/gateway.Dockerfile

@@ -5,18 +5,27 @@ RUN corepack enable
 
 FROM base AS builder
 WORKDIR /app
+# Copy workspace manifests first for layer-cached install
 COPY pnpm-workspace.yaml pnpm-lock.yaml package.json ./
 COPY apps/gateway/package.json ./apps/gateway/
 COPY packages/ ./packages/
+COPY plugins/ ./plugins/
 RUN pnpm install --frozen-lockfile
 COPY . .
-RUN pnpm --filter @mosaic/gateway build
+# Build gateway and all of its workspace dependencies via turbo dependency graph
+RUN pnpm turbo run build --filter @mosaicstack/gateway...
+# Produce a self-contained deploy artifact: flat node_modules, no pnpm symlinks
+# --legacy is required for pnpm v10 when inject-workspace-packages is not set
+RUN pnpm --filter @mosaicstack/gateway --prod deploy --legacy /deploy
 
 FROM base AS runner
 WORKDIR /app
 ENV NODE_ENV=production
+# Use the pnpm deploy output — resolves all deps into a flat, self-contained node_modules
+COPY --from=builder /deploy/node_modules ./node_modules
+COPY --from=builder /deploy/package.json ./package.json
+# dist is declared in package.json "files" so pnpm deploy copies it into /deploy;
+# copy from builder explicitly as belt-and-suspenders
 COPY --from=builder /app/apps/gateway/dist ./dist
-COPY --from=builder /app/apps/gateway/package.json ./package.json
-COPY --from=builder /app/node_modules ./node_modules
 EXPOSE 4000
 CMD ["node", "dist/main.js"]