feat: Phase 4.5 — Déploiement multi-plateforme v0.4.5

- service.v: --install-service / --uninstall-service / --service-status
  Windows (sc.exe SCM), Linux systemd, Linux openrc — auto-détection OS
- main.v: nouveaux flags service, help mis à jour
- Dockerfile: multi-stage (V from source → alpine:3.20 minimal)
- docker-compose.yml: prêt à l'emploi avec healthcheck
- scripts/install.sh: one-liner Linux (detect OS/arch, build, install)
- scripts/install.ps1: one-liner Windows PowerShell

Docs: ROADMAP Phase 4.5 marqué DONE, version 0.4.5

v.mod

@@ -1,7 +1,7 @@
 Module {
     name: 'ntfy-bridge'
     description: 'Homelab notification hub — aggregates Gitea, Docker, Uptime Kuma → Ntfy'
-    version: '0.4.0'
+    version: '0.4.5'
     license: 'MIT'
     dependencies: []
     subdirs: ['sources']