Move shared infrastructure to a separate Infrastructure repo

Postgres, Zitadel, SeaweedFS, RabbitMQ and Jaeger no longer run as part
of this stack. They're shared services (used by Musify, Ping and
docker-manager) that now live in a separate Infrastructure repository
and must already be running.

deploy/compose.yml keeps only what's specific to Musify: its own
database connection, its own OIDC app and storage bucket (created
against the shared Zitadel/SeaweedFS via zitadel-init/seaweedfs-init),
and the application containers. A new wait-for-postgres one-shot
replaces the in-file Postgres health check, which no longer works now
that Postgres lives in a different compose project.

compose.prod.yml joins Infrastructure's infra-net network instead of
running its own copies. Docs and READMEs updated to match.

deploy/.env.prod.example

@@ -3,11 +3,14 @@
 #
 #   1. replace every `example.com` with your domain,
 #   2. replace every CHANGE_ME with a strong random value
-#      (`openssl rand -hex 24`; the Zitadel masterkey needs exactly 32 chars),
+#      (`openssl rand -hex 24`),
 #   3. point these DNS records at the server, all proxied/TLS-terminated the
 #      same way: example.com, www, api, auth, stream, s3.
 #
-# Not versioned. Keep it readable only by the deploy user (chmod 600).
+# Requires ../../../Infrastructure running first, on the same Docker host,
+# with its own `infra-net` network already created. See
+# ../../../Infrastructure/README.md. Not versioned. Keep it readable only by
+# the deploy user (chmod 600).
 
 DOTNET_ENVIRONMENT=Production
 
@@ -20,22 +23,15 @@ PUBLIC_STREAM_URL=https://stream.example.com
 PUBLIC_AUTH_URL=https://auth.example.com
 S3_PUBLIC_URL=https://s3.example.com
 
-# --- PostgreSQL (shared by Musify and Zitadel) -------------------------------
+# --- PostgreSQL (Infrastructure's shared instance, Musify's own database) ---
+# POSTGRES_USER / POSTGRES_PASSWORD must match Infrastructure's .env.prod.
+POSTGRES_HOST=postgres
 POSTGRES_USER=postgres
 POSTGRES_PASSWORD=CHANGE_ME
 POSTGRES_DB=musify_db
 
-# --- Zitadel (OIDC) ----------------------------------------------------------
-# The masterkey MUST be exactly 32 characters and can never be rotated in place.
-ZITADEL_MASTERKEY=CHANGE_ME_32_CHARACTERS_EXACTLY_
-ZITADEL_EXTERNAL_DOMAIN=auth.example.com
-ZITADEL_EXTERNAL_PORT=443
-ZITADEL_EXTERNAL_SECURE=true
-ZITADEL_DATABASE_PASSWORD=CHANGE_ME
-# Console login: <username>@zitadel.<external domain>
-ZITADEL_ADMIN_USERNAME=admin
-ZITADEL_ADMIN_PASSWORD=CHANGE_ME
-# Keep OIDC apps strict about https redirect URIs in production.
+# --- Zitadel (OIDC, shared instance) -----------------------------------------
+ZITADEL_ADMIN_PAT_DIR=../../../Infrastructure/zitadel/.output
 ZITADEL_DEV_MODE=false
 
 # OIDC clients: the zitadel-init one-shot service (see compose.yml) fills
@@ -44,16 +40,22 @@ AUTH_CLIENT_ID=
 WEB_CLIENT_ID=
 WEB_CLIENT_SECRET=
 
-# --- RabbitMQ (MassTransit) --------------------------------------------------
+# --- RabbitMQ (shared instance, MassTransit) --------------------------------
+RABBITMQ_HOST=rabbitmq
 RABBITMQ_DEFAULT_USER=musify
 RABBITMQ_DEFAULT_PASS=CHANGE_ME
 
-# --- SeaweedFS (S3) ----------------------------------------------------------
+# --- SeaweedFS (S3, shared instance, Musify's own bucket) --------------------
+SEAWEEDFS_HOST=seaweedfs
 S3_ACCESS_KEY=CHANGE_ME
 S3_SECRET_KEY=CHANGE_ME
 S3_BUCKET=webapi-storage
+S3_INTERNAL_URL=http://seaweedfs:8333
 S3_USE_HTTP=false
 
+# --- Jaeger (shared instance, tracing) ---------------------------------------
+JAEGER_HOST=jaeger
+
 # --- Web player --------------------------------------------------------------
 # Key material for the encrypted session cookie. Rotating it logs everyone out.
 SESSION_SECRET=CHANGE_ME