feat: am ai — langage naturel vers action shell securisee via AIChat (issues #96 #97)

- Commande am ai (alias CLI: am shell) : conversationnel par defaut
  (aichat -f <ctx> "<prompt>"), mode --exec avec generation aichat --dry-run
- Securite (issue #97) : classification safe/risky + certainite affichee,
  politique dry-run par defaut (settings.shell_ai.default_safety:
  dry-run | confirm | auto), confirmation y/N pour les commandes risky,
  --yes pour executer, --dry-run force la simulation
- Flags : --exec/-e, --files/-f (defaut: dossier courant), --provider,
  --model (registre providers -> env aichat + modele, token via keyring)
- Execution via le shell utilisateur (default_shell > SHELL > COMSPEC)
- Journalisation : EventKind::ShellAi (mode, risk, certainty, executed)
- Module src/shell_ai.rs (classification, politique, generation, execution)
- Câblage complet : cli, dispatch, help, REPL (parseur+completer+banner),
  tip, man pages (am-ai.1), i18n EN, config.yaml (bloc shell_ai)
- Tests : 7 unitaires (classification, certainty, extraction, decision)
  + 4 integration (shim aichat.cmd : dry-run par defaut, --yes, mode
  conversationnel, mode confirm) — 339 tests verts
- v1.0.5 ; ROADMAP axe 13.3 coche (6 lignes), epic #93 clôturee

closes #93
closes #96
closes #97

src/cli.rs

@@ -214,6 +214,9 @@ pub enum Command {
         #[arg(long)]
         yes: bool,
     },
+    /// Langage naturel → action shell via AIChat (issues #96 #97); alias: shell
+    #[command(alias = "shell")]
+    Ai(AiArgs),
     /// Start an agent (foreground by default, or detached with --background)
     Start(StartArgs),
     /// Stop a background agent (SIGTERM, then SIGKILL after the timeout)
@@ -700,6 +703,35 @@ pub struct WebArgs {
     pub no_open: bool,
 }
 
+/// Arguments of am ai (issues #96 #97): natural language → shell action
+/// via AIChat. The global flags --dry-run and --yes/-y apply as well.
+#[derive(Args, Debug, Clone, Default)]
+pub struct AiArgs {
+    /// The request in natural language
+    #[arg(value_name = "PROMPT", num_args = 1.., required = true)]
+    pub prompt: Vec<String>,
+    /// Execute the generated shell command (after the safety policy)
+    #[arg(short = 'e', long, action = ArgAction::SetTrue)]
+    pub exec: bool,
+    /// Files or directories passed as context (repeatable; default: the
+    /// current directory)
+    #[arg(short = 'f', long = "files", value_name = "PATH", action = ArgAction::Append)]
+    pub files: Vec<std::path::PathBuf>,
+    /// Provider of the registry used by aichat (env vars + model)
+    #[arg(long, value_name = "ID")]
+    pub provider: Option<String>,
+    /// Force a model (aichat --model)
+    #[arg(long, value_name = "MODEL")]
+    pub model: Option<String>,
+    /// REPL-only: --yes given on the REPL line (the CLI global -y/--yes is
+    /// handled by clap directly).
+    #[arg(skip)]
+    pub yes: bool,
+    /// REPL-only: --dry-run given on the REPL line.
+    #[arg(skip)]
+    pub dry_run: bool,
+}
+
 /// Arguments of am serve (issue #80).
 #[derive(Args, Debug, Clone, Default)]
 pub struct ServeArgs {