feat: phase 2 — am lab (benchmark N agents) + plugins d'événements (contrat JSON)

- #62: am lab --agents a,b --task <f> — séquentiel ou --parallel, capture
  durée/exit/sortie/coût estimé, rapport comparatif tableau + --json stable,
  tâches versionnables dans <state>/lab/ (--list), rejouables à l'identique
- #75: plugins/ sous state_dir, déclenchés sur on_install/on_start/on_stop/
  on_update (App::emit), contrat JSON stdin/stdout, timeout configurable,
  échec non bloquant, garde anti-récursion AM_PLUGINS_RUNNING, am plugins
  + am plugins --test <name> (CI), exemples notify + ci-webhook
- intégration REPL (parse, complétion, bannière, is_am_command), help, tips,
  man pages (am-lab.1, am-plugins.1), README, ROADMAP (26/27), v0.5.4
- 334 tests verts (309 + 25)

closes #62
closes #75

src/repl.rs

@@ -116,6 +116,8 @@ const COMMAND_DESCRIPTIONS: &[(&str, &str)] = &[
     ("sync", "push the state (journal, sessions, config) into a git repo"),
     ("migrate", "export/import a machine transfer bundle (config + state)"),
     ("playbook", "replay a saved history sequence step by step (am history --save)"),
+    ("lab", "benchmark the same task on several agents (duration, cost, --json)"),
+    ("plugins", "list the event plugins and test one (JSON contract on stdin/stdout)"),
     ("shell", "show or switch the system shell"),
     ("theme", "show or switch the color theme"),
     ("tip", "cheat sheet of the most useful commands"),
@@ -230,7 +232,7 @@ impl AmCompleter {
                 "self-update", "self-uninstall", "export", "import", "shell", "theme",
                 "tip", "dashboard", "favorite", "unfavorite", "note", "tag", "untag", "tags",
                 "profile", "man", "models", "catalog", "suggest", "audit",
-                "service", "schedule", "monitor", "sync", "migrate", "playbook",
+                "service", "schedule", "monitor", "sync", "migrate", "playbook", "lab", "plugins",
                 "ls", "dir", "cd", "ps", "where", "get", "help", "version", "exit",
             ],
             config_sub: vec!["show", "path", "edit", "validate", "add"],
@@ -782,6 +784,9 @@ pub fn banner_box(
     rows.push(inner(
         "  automate   service install · schedule add · doctor --watch · monitor · sync · migrate · playbook".to_string(),
     ));
+    rows.push(inner(
+        "  bench      lab --agents a,b --task t.yaml · plugins · plugins --test <name>".to_string(),
+    ));
     rows.push(inner(
         "  system     self-update · self-uninstall · export · import".to_string(),
     ));
@@ -1617,6 +1622,16 @@ fn handle_line(
                     .collect(),
             }
         },
+        "lab" => Command::Lab(crate::cli::LabArgs {
+            agents: opt_value("--agents"),
+            task: opt_value("--task").map(std::path::PathBuf::from),
+            parallel: flag("--parallel"),
+            timeout: opt_value("--timeout").and_then(|v| v.parse().ok()),
+            list: flag("--list"),
+        }),
+        "plugins" => Command::Plugins(crate::cli::PluginsArgs {
+            test: opt_value("--test"),
+        }),
         "init" => Command::Init {
             force: flag("--force"),
             template: opt_value("--template"),
@@ -1864,6 +1879,8 @@ pub fn is_am_command(word: &str) -> bool {
             | "sync"
             | "migrate"
             | "playbook"
+            | "lab"
+            | "plugins"
     )
 }