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

man/am.1

@@ -1,6 +1,6 @@
 .ie \n(.g .ds Aq \(aq
 .el .ds Aq '
-.TH am 1  "am 1.0.3" 
+.TH am 1  "am 1.0.5" 
 .SH NAME
 am \- agent\-manager (am) — manage local AI coding agents
 .SH SYNOPSIS
@@ -133,6 +133,9 @@ Suggest agents matching a query, boosted by real usage (issue #61)
 am\-ask(1)
 Ask a natural\-language request and get the matching am command(s) (issue #78): local rules first, optional LLM refinement, confirmation before execution
 .TP
+am\-ai(1)
+Langage naturel → action shell via AIChat (issues #96 #97); alias: shell
+.TP
 am\-start(1)
 Start an agent (foreground by default, or detached with \-\-background)
 .TP
@@ -244,4 +247,4 @@ Export the configuration and installation state (backup)
 am\-import(1)
 Import a previously exported configuration and state
 .SH VERSION
-v1.0.3
+v1.0.5