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

scripts/example-plugin-disk.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+# Example ntfy-bridge plugin — disk space checker
+#
+# A plugin receives nothing on stdin (when polled) and outputs a JSON
+# Event object on stdout. Exit 0 = send, exit 1 = skip/drop.
+#
+# Fields: source, name, topic, priority (1-5), message, tags[], click_url, actions[]
+
+THRESHOLD=90
+USAGE=$(df -h / | tail -1 | awk '{print $5}' | sed 's/%//')
+
+if [ "$USAGE" -lt "$THRESHOLD" ]; then
+  # No alert needed — exit non-zero to skip
+  exit 1
+fi
+
+# Output a JSON Event to stdout
+cat <<EOF
+{
+  "source": "plugin",
+  "name": "disk-check",
+  "topic": "daily",
+  "priority": 4,
+  "message": "💾 **Disk usage: ${USAGE}%**\nThreshold: ${THRESHOLD}%\nHost: $(hostname)",
+  "tags": ["warning"]
+}
+EOF