Containerise for Dokploy, and a demo login that survives production

Everything needed to build and run this on Dokploy at
linkdr.serfaty.site, plus the two things that turned out to be broken
the moment it left a laptop.

The build did not work in a container at all. `lib/auth.ts` throws when
AUTH_SECRET or NEXT_PUBLIC_APP_URL is missing — correct at boot, wrong
during `next build`, which imports every route module with
NODE_ENV=production and none of the runtime secrets. The only way past
it was baking a session key into an image layer, which is worse than
the problem the guard exists to prevent. Both checks now skip
NEXT_PHASE=phase-production-build and still fire on a real boot.

Corepack in node:22.12-alpine ships expired npm registry signing keys
and dies before it can download pnpm, so the image installs corepack
first and prepares the pinned version explicitly.

The image is the standalone trace, which needs outputFileTracingRoot at
the REPO root: pnpm hoists to a root .pnpm store and tracing from
apps/web silently omits every workspace package. 427MB, runs as
non-root, and its healthcheck talks to Postgres — a container that
cannot reach its database must never enter rotation, because a deploy
that goes green and then 500s does not roll back.

DEMO_LOGIN is a login bypass under NODE_ENV=production and there is no
honest way to describe it otherwise. It is a separate variable from
ALLOW_DEV_LOGIN so that copying a dev .env into a real environment
cannot enable it by accident, it still only affects the one seeded
number, and it prints a boot warning every single start so it cannot be
forgotten. That deployment holds nothing but fixtures. It comes out
before the platform sees a real signup.

Also: /api/health, and next/image hosts corrected to the Spaces bucket
rather than the R2 one this stopped using.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.env.example

@@ -97,9 +97,19 @@ NEXT_PUBLIC_CITY_LAT=19.4326
 NEXT_PUBLIC_CITY_LNG=-99.1332
 TWILIO_FROM_NUMBER=
 
-# Dev-only fixed login (+34600000000 / code 000000). MUST stay false/unset in production.
+# Dev-only fixed login (+52 55 0000 0000 / code 000000). Ignored entirely when
+# NODE_ENV=production, so this cannot leak a bypass into a real deployment.
 ALLOW_DEV_LOGIN=false
 
+# The SAME fixed login, deliberately allowed in a production build, for the
+# client-demo deployment only. Separate from ALLOW_DEV_LOGIN so that copying a
+# developer's .env into a real environment cannot switch it on by accident.
+#
+# Only +52 55 0000 0000 is affected; every other number still goes through
+# Twilio. Prints a loud warning on every boot. MUST be unset before this
+# platform accepts a real signup — see server/dev-login.ts.
+DEMO_LOGIN=false
+
 # Bugsink (Sentry-compatible error tracking). Write-only ingest key, safe in the
 # client bundle. Leave blank to disable reporting entirely.
 NEXT_PUBLIC_SENTRY_DSN=