feat: v0.7.0 — AgentDef provider/model + install --provider/--model/--no-config : résolution flag > agent > défaut, erreur si provider inconnu (liste du registre), warning si modèle absent, résolution affichée en résumé et au --dry-run (closes #90)

- Providers réels livrés dans le catalogue par défaut (anthropic★/openai/deepseek/google) + hints provider sur claude-code/deepseek-harness
- Suppression par null dans l'overlay : am providers remove écrit <nom>: null (merge traite null comme suppression, set_path remplace le null avant de descendre)
- Cascade @secret (#89) : le provider déclaré de l'agent prime sur default_provider

src/help.rs

@@ -797,11 +797,14 @@ pub static HELP_SPECS: &[HelpSpec] = &[
         name: "install",
         category: "Commands",
         usage: "install {flags} <agent>",
-        about: "Install an agent and its dependencies.",
-        search_terms: &["add", "setup"],
+        about: "Install an agent and its dependencies, and resolve its LLM provider + model (issue #90): --provider > agent.provider > settings.default_provider; --model > agent.model > provider.default_model.",
+        search_terms: &["add", "setup", "provider", "model"],
         flags: &[
             HelpFlag { short: "", long: "--method", value: "METHOD", desc: "Select the install method (index, or type: npm, pip, uv, cargo, go, bun, curl, binary, git)" },
             HelpFlag { short: "", long: "--force", value: "", desc: "Reinstall even if already installed" },
+            HelpFlag { short: "", long: "--provider", value: "PROVIDER", desc: "Provider to configure (default: the agent's provider, else settings.default_provider)" },
+            HelpFlag { short: "", long: "--model", value: "MODEL", desc: "Model to configure (default: the provider's default model)" },
+            HelpFlag { short: "", long: "--no-config", value: "", desc: "Skip the post-install provider configuration (issue #91)" },
         ],
         subcommands: &[],
         parameters: &[
@@ -812,6 +815,9 @@ pub static HELP_SPECS: &[HelpSpec] = &[
             HelpExample { desc: "Install an agent with its dependencies.", code: "install claude-code" },
             HelpExample { desc: "Pick a specific install method.", code: "install smelt --method uv" },
             HelpExample { desc: "Reinstall over an existing install.", code: "install claude-code --force" },
+            HelpExample { desc: "Force a provider and a model.", code: "install agentty --provider deepseek --model deepseek-reasoner" },
+            HelpExample { desc: "Preview the resolved provider/model without installing.", code: "install agentty --dry-run" },
+            HelpExample { desc: "Install without any post-install configuration.", code: "install agentty --no-config" },
         ],
     },
     HelpSpec {