feat(deploy): add self-hosted homelab deploy toolkit

- deploy/deploy.sh: idempotent deploy script with dynamic port
  allocation (3011..30200), flock-based concurrency, atomic
  .postgrest-port/.nextjs-port writes, port cleanup of the previous
  deploy + dev stack, nginx config rendering+reload, healthchecks
  with rollback, optional image pruning
- deploy/docker-compose.yml + Dockerfile.nextjs: example stack
  consuming ${POSTGREST_HOST_PORT} / ${NEXTJS_HOST_PORT} (kept as
  reference; the repo's root docker-compose.yml is the source of
  truth for the actual production stack)
- deploy/nginx.conf.template: /api/* -> PostgREST, /* -> Next.js
- deploy/.env.production.example: managed port block + preserved secrets
- deploy/healthcheck.sh: standalone health probe (cron-friendly)
- deploy/Makefile: deploy/status/health/logs/down/rollback targets
- deploy/GITEA_SETUP.md: webhook vs Actions runner instructions
- deploy/README.md + deploy/.gitignore

Note: .gitea/workflows/deploy.yml was deliberately not added — the
existing workflow at that path on Gitea main is the source of truth
and is left untouched.

deploy/.env.production.example

@@ -0,0 +1,40 @@
+# =============================================================================
+# .env.production — secrets + dynamic ports for the running containers
+# =============================================================================
+#
+# deploy.sh writes the first three lines on every successful deploy.
+# Everything below is YOUR responsibility to populate. deploy.sh preserves
+# unknown lines verbatim across deploys (it only overwrites the lines it
+# knows about), so you can safely commit this file to a private repo or
+# provision it via your secrets manager of choice.
+#
+# In production, this file should be mode 0600 and owned by the deploy user.
+# =============================================================================
+
+# --- managed by deploy.sh (do not edit by hand) -------------------------------
+POSTGREST_HOST_PORT=3011
+NEXTJS_HOST_PORT=3012
+NEXT_PUBLIC_API_URL=http://localhost:3011
+
+# --- PostgREST connection ---------------------------------------------------
+PGRST_DB_URI=postgres://app:secret@db.internal:5432/app_production
+PGRST_DB_ANON_ROLE=anon
+PGRST_DB_SCHEMA=public
+
+# --- Next.js server-side secrets -------------------------------------------
+# Anything not prefixed NEXT_PUBLIC_ is server-only and read at request time.
+DATABASE_URL=postgres://app:secret@db.internal:5432/app_production
+NEXTAUTH_SECRET=change-me-to-a-long-random-string
+NEXTAUTH_URL=https://app.example.com
+SESSION_SECRET=change-me-too
+
+# --- External services ------------------------------------------------------
+STRIPE_SECRET_KEY=sk_live_replace_me
+STRIPE_PUBLISHABLE_KEY=pk_live_replace_me
+STRIPE_WEBHOOK_SECRET=whsec_replace_me
+
+SMTP_HOST=smtp.example.com
+SMTP_PORT=587
+SMTP_USER=apikey
+SMTP_PASSWORD=replace_me
+SMTP_FROM="My App <noreply@example.com>"