Add HarborForge stack to docker-compose

- Add hf_db_init sidecar that ensures the HarborForge database exists on
  every `compose up` (idempotent CREATE DATABASE IF NOT EXISTS), so the
  shared MySQL instance can host both hangmanlab and harborforge schemas
  without touching existing data.
- Wire hf_backend's DATABASE_URL directly from compose env vars and gate
  it on hf_db_init completing successfully.
- Add a mysqladmin-ping healthcheck on mysql so dependents can wait on
  service_healthy.
- Drop dead Vite runtime envs from hf_frontend (build-time only) and
  make wizard CORS_ORIGINS configurable via HF_FRONTEND_HOST.
- Seed .env.example with all variables the stack reads.

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

.env.example

@@ -0,0 +1,32 @@
+# --- HangmanLab backend / frontend ---
+BACKEND_PORT=8000
+FRONTEND_PORT=80
+
+# --- MySQL (shared by hangmanlab-backend and HarborForge) ---
+DB_PORT=3306
+DB_NAME=hangmanlab
+DB_USER=hangmanlab
+DB_PASSWORD=change_me
+MYSQL_ROOT_PASSWORD=change_me_root
+
+# --- HarborForge ---
+HF_BACKEND_PORT=8001
+HF_FRONTEND_PORT=3000
+HF_FRONTEND_DEV_MODE=0
+HF_SECRET_KEY=change_me_in_production
+HF_LOG_LEVEL=INFO
+
+# Database name used by HarborForge (created automatically by hf_db_init on every up).
+HF_DB_NAME=harborforge
+
+# Browser-facing origin of the HarborForge frontend. Used as the AbstractWizard
+# CORS allow-list. Must match the scheme/host/port the user types in their
+# browser. Examples:
+#   http://localhost:3000
+#   https://harborforge.example.com
+# Multiple origins can be comma-separated.
+HF_FRONTEND_HOST=http://localhost:3000
+
+# AbstractWizard SSH-tunnel port (server-side bind). The setup wizard in the
+# browser will ask the user to enter the matching local port.
+WIZARD_PORT=8080