Point at the shared Infrastructure repo instead of Musify's folder

Ping already reused Musify's Zitadel and SeaweedFS, but did so through a
hardcoded relative path into Musify's own deploy folder
(../../../Musify/MusifyM/deploy/zitadel/.output), which only worked
because Musify happened to be the one running them. Those services now
live in a separate Infrastructure repository instead, so this points
there.

Also drops Ping's own Postgres container in favor of Infrastructure's
shared instance (its own ping_db database), with a wait-for-postgres
one-shot replacing the in-file health check.

backend/deploy/.env.example

@@ -1,29 +1,32 @@
 # Development configuration for deploy/compose.yml + compose.dev.yml.
-# Copy to deploy/.env and adjust. Not versioned.
+# Copy to deploy/.env and adjust.
 #
 #   cp deploy/.env.example deploy/.env
+#
+# Requires ../../../Infrastructure running first (Postgres, Zitadel,
+# SeaweedFS). See ../../../Infrastructure/README.md. Everything marked
+# "must match Infrastructure's .env" below has to be the same value as the
+# one in that file.
 
 DOTNET_ENVIRONMENT=Development
 
 # --- Public URLs -------------------------------------------------------------
 PUBLIC_WEB_URL=http://localhost:3100
 PUBLIC_API_URL=http://localhost:5211
-
-# Ping reuses the Zitadel and SeaweedFS instances already running for Musify instead of
-# spinning up its own, so this must match Musify's PUBLIC_AUTH_URL exactly.
 PUBLIC_AUTH_URL=http://host.docker.internal:8080
 
-# --- PostgreSQL (Ping's own database — Zitadel keeps using Musify's) --------
+# --- PostgreSQL (Infrastructure's shared instance, Ping's own database) -----
+# POSTGRES_USER / POSTGRES_PASSWORD must match Infrastructure's .env.
+POSTGRES_HOST=host.docker.internal
 POSTGRES_USER=postgres
 POSTGRES_PASSWORD=postgres
 POSTGRES_DB=ping_db
-POSTGRES_HOST_PORT=59010
 
-# --- Zitadel (shared with Musify) --------------------------------------------
-# zitadel-init needs Musify's admin service-account PAT to create Ping's own project/apps
-# in that same Zitadel instance. Point this at Musify's deploy/zitadel/.output folder —
-# adjust if your Musify checkout lives somewhere else relative to this one.
-ZITADEL_ADMIN_PAT_DIR=../../../Musify/MusifyM/deploy/zitadel/.output
+# --- Zitadel (OIDC, shared instance) -----------------------------------------
+# Path to the admin service-account PAT Infrastructure's Zitadel writes on
+# init. Adjust if your Infrastructure checkout lives somewhere else relative
+# to this one.
+ZITADEL_ADMIN_PAT_DIR=../../../Infrastructure/zitadel/.output
 ZITADEL_DEV_MODE=true
 
 # OIDC clients: the zitadel-init one-shot service (see compose.yml) fills these in
@@ -31,9 +34,8 @@ ZITADEL_DEV_MODE=true
 AUTH_CLIENT_ID=
 WEB_CLIENT_ID=
 
-# --- SeaweedFS (S3, shared with Musify) --------------------------------------
-# Same SeaweedFS instance as Musify, so these must be the REAL values from Musify's own
-# deploy/.env (S3_ACCESS_KEY / S3_SECRET_KEY) — not the placeholders below.
+# --- SeaweedFS (S3, shared instance, Ping's own bucket) ----------------------
+# S3_ACCESS_KEY / S3_SECRET_KEY must match Infrastructure's .env.
 S3_ACCESS_KEY=admin_access_key
 S3_SECRET_KEY=admin_secret_key
 S3_BUCKET=ping-storage
@@ -41,9 +43,7 @@ S3_PUBLIC_URL=http://host.docker.internal:8333
 S3_USE_HTTP=true
 
 # --- LiveKit (voice/video SFU) ------------------------------------------------
-# Overrides --dev's built-in "devkey/secret" pair (see compose.yml's LIVEKIT_KEYS): the
-# LiveKit .NET server SDK rejects secrets shorter than 256 bits. Generate your own with:
-#   $b = [byte[]]::new(32); [System.Security.Cryptography.RandomNumberGenerator]::Create().GetBytes($b); [Convert]::ToBase64String($b)
+# --dev mode uses this fixed dev key pair; fine for local development only.
 LIVEKIT_API_KEY=devkey
 LIVEKIT_API_SECRET=9U1eDtZx9eQrSWern4UcWa3lYIrfvrQqExLlkUXpP+o=