feat: v0.6.0 — ACLs multi-utilisateurs + Plugin system

**ACLs (Access Control Lists):**
- Ajout du type AclConfig dans sources/event.v (allowed_ips CIDR + allowed_tokens)
- Chaque source webhook (Gitea, Uptime Kuma, Cron, Generic) supporte les ACLs
- Validation IP via X-Forwarded-For / X-Real-IP avant HMAC
- Validation Bearer token via Authorization header
- Tests: 7 tests ACL (IP exact, CIDR, parse IPv4, ACL vide, IP+token combiné)

**Plugin system:**
- sources/plugin.v: runner exécutable externe, stdout JSON → Event
- Exit 0 = publish, exit ≠ 0 = skip. Timeout configurable
- Plugin loop dans server.v (goroutine, toutes les 60s)
- Example: scripts/example-plugin-disk.sh (vérifie espace disque)

**Docs:**
- README.md: ajout source Plugin + section Features complète
- ARCHITECTURE.md: flux Plugin, flux ACL, endpoints /metrics /api/silence
- ROADMAP.md: Phase 5 → 8/8 complet, ajout v0.6.0
- ntfy-bridge.example.yaml: sections ACLs et Plugins commentées
- Version bump: 0.5.0 → 0.6.0

webhook.v

@@ -6,6 +6,7 @@ pub enum SourceKind {
 	uptime_kuma
 	cron
 	generic
+	plugin
 }
 
 pub struct WebhookRoute {
@@ -42,6 +43,11 @@ pub fn build_webhook_routes(cfg Config) map[string]WebhookRoute {
 			index: i
 		}
 	}
+	for i, _ in cfg.sources.plugin {
+		// Plugin sources don't have webhook_path — they run as background tasks
+		// Reserved for future webhook-triggered plugin support
+		_ = i
+	}
 
 	return routes
 }