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/healthcheck.sh

@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+# =============================================================================
+# healthcheck.sh — standalone, callable from cron / monitoring
+# =============================================================================
+#
+# Reads the current prod ports from .postgrest-port / .nextjs-port and curls
+# each service. Exit code is the count of failed checks (0 = all healthy).
+#
+# Usage:
+#   ./healthcheck.sh
+#   ./healthcheck.sh --nginx      # also check the fronted URL
+#   WORKSPACE=/srv/app ./healthcheck.sh
+# =============================================================================
+
+set -Eeuo pipefail
+IFS=$'\n\t'
+
+WORKSPACE="${WORKSPACE:-$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)}"
+POSTGREST_PORT_FILE="${POSTGREST_PORT_FILE:-${WORKSPACE}/.postgrest-port}"
+NEXTJS_PORT_FILE="${NEXTJS_PORT_FILE:-${WORKSPACE}/.nextjs-port}"
+TIMEOUT="${HEALTHCHECK_TIMEOUT:-5}"
+
+failures=0
+
+check() {
+  local label="$1" url="$2"
+  if curl -fsS --max-time "$TIMEOUT" -o /dev/null "$url"; then
+    printf '  [ OK ] %-20s %s\n' "$label" "$url"
+  else
+    printf '  [FAIL] %-20s %s\n' "$label" "$url"
+    failures=$(( failures + 1 ))
+  fi
+}
+
+pgrest_port=$(tr -d '[:space:]' < "$POSTGREST_PORT_FILE" 2>/dev/null || echo "")
+next_port=$(tr -d '[:space:]' < "$NEXTJS_PORT_FILE" 2>/dev/null || echo "")
+
+if [[ -n "$pgrest_port" ]]; then
+  check "postgrest" "http://127.0.0.1:${pgrest_port}/"
+else
+  printf '  [SKIP] postgrest          (no .postgrest-port)\n'
+fi
+
+if [[ -n "$next_port" ]]; then
+  check "nextjs"    "http://127.0.0.1:${next_port}/"
+else
+  printf '  [SKIP] nextjs             (no .nextjs-port)\n'
+fi
+
+if [[ "${1:-}" == "--nginx" ]]; then
+  check "nginx" "http://127.0.0.1/"
+fi
+
+exit "$failures"