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

sources/event.v

@@ -35,6 +35,13 @@ pub:
 	clear  bool // whether to dismiss notification after action
 }
 
+// v0.6 — ACL per webhook path
+pub struct AclConfig {
+pub mut:
+	allowed_ips    []string @[json: 'allowed_ips']    // CIDR ranges or single IPs
+	allowed_tokens []string @[json: 'allowed_tokens'] // bearer tokens
+}
+
 pub struct GiteaSource {
 pub mut:
 	name         string         @[json: 'name']
@@ -44,6 +51,7 @@ pub mut:
 	priority_map map[string]int @[json: 'priority_map']
 	tags         []string       @[json: 'tags']
 	repo         string         @[json: 'repo']
+	acl          AclConfig      @[json: 'acl']
 }
 
 pub struct UptimeKumaState {
@@ -61,6 +69,7 @@ pub mut:
 	priority_map map[string]int             @[json: 'priority_map']
 	tags         []string                   @[json: 'tags']
 	state_map    map[string]UptimeKumaState @[json: 'state_map']
+	acl          AclConfig                  @[json: 'acl']
 }
 
 pub struct DockerSource {
@@ -99,6 +108,7 @@ pub mut:
 	template     string         @[json: 'template']
 	priority_map map[string]int @[json: 'priority_map']
 	tags         []string       @[json: 'tags']
+	acl          AclConfig      @[json: 'acl']
 }
 
 pub struct GenericSource {
@@ -109,6 +119,17 @@ pub mut:
 	template     string         @[json: 'template']
 	priority_map map[string]int @[json: 'priority_map']
 	tags         []string       @[json: 'tags']
+	acl          AclConfig      @[json: 'acl']
+}
+
+// v0.6 — Plugin source: external executable that receives JSON on stdin, outputs JSON on stdout
+pub struct PluginSource {
+pub mut:
+	name    string    @[json: 'name']
+	topic   string    @[json: 'topic']
+	command string    @[json: 'command'] // path to executable
+	timeout int       @[json: 'timeout'] // seconds (default: 10)
+	acl     AclConfig @[json: 'acl']
 }
 
 // render_source_template applies variable substitution to a template string.