docs(deploy): add install guide for a domain with HTTPS

- docs/install-guide.md: step-by-step server setup (DNS, Docker, install.sh,
  .env, launch, checks), web and Android client setup, own reverse proxy
  variant, updates, backups and troubleshooting
- deploy/compose.tls.yaml + Caddyfile: optional Caddy with automatic
  Let's Encrypt in front of nginx (enabled via COMPOSE_FILE in .env)
- nginx: honour X-Forwarded-Proto/For from private networks
- .env.example: DOMAIN, ACME_EMAIL, COMPOSE_FILE, bootstrap admin vars
- install.sh: create caddy data dirs; release.yml: ship TLS files as assets
- deployment.md, docs index and README link to the guide

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/README.md

@@ -22,7 +22,8 @@ Pipu Music — self-hosted музыкальный сервис (веб + Android
 | [i18n.md](i18n.md) | Локализация (ru / en, расширяемость) |
 | [testing.md](testing.md) | Стратегия тестирования |
 | [ci-cd.md](ci-cd.md) | Gitea Actions: проверки и релиз по тегу |
-| [deployment.md](deployment.md) | Docker Compose, конфигурация, бэкапы |
+| [install-guide.md](install-guide.md) | **Пошагово:** установка сервера на домен с HTTPS, подключение веба и Android |
+| [deployment.md](deployment.md) | Справочник по развёртыванию: сервисы, каталоги, переменные, бэкапы |
 | [conventions.md](conventions.md) | Соглашения по коду, git, версиям |
 | [roadmap.md](roadmap.md) | Этапы разработки и критерии готовности |