fix(model): require confirmation for expensive model selections

Rebased onto current main and re-ported across the restructured
surfaces: model flows now thread confirm_provider/base_url/api_key
through hermes_cli/model_setup_flows.py, the Discord picker lives in
plugins/platforms/discord/adapter.py, and the web dashboard picker
applies chat-mode switches via config.set so the expensive-model
confirmation can ride the response.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/src/lib/api.ts

@@ -1763,9 +1763,12 @@ export interface AuxiliaryModelsResponse {
 }
 
 export interface ModelAssignmentRequest {
+  confirm_expensive_model?: boolean;
   scope: "main" | "auxiliary";
   provider: string;
   model: string;
+  /** Optional OpenAI-compatible endpoint URL for custom/local main providers. */
+  base_url?: string;
   /** For auxiliary: task slot name, "" for all, "__reset__" to reset all. */
   task?: string;
 }
@@ -1779,6 +1782,8 @@ export interface StaleAuxAssignment {
 }
 
 export interface ModelAssignmentResponse {
+  confirm_message?: string;
+  confirm_required?: boolean;
   ok: boolean;
   scope?: string;
   provider?: string;