feat: refine language controls and add per-tier ChatGPT Fast mode

src/core/settings.ts

@@ -193,6 +193,8 @@ export interface ModelSlot {
 	model?: { provider: string; id: string };
 	/** The thinking budget swap. */
 	thinkingLevel?: ThinkingLevel;
+	/** Opt-in ChatGPT priority processing for this tier. Absent = off. */
+	fastMode?: boolean;
 }
 
 /** The `models` settings section (owner decision 2026-09-20: a dedicated
@@ -490,7 +492,13 @@ function sanitizeModels(raw: Record<string, unknown>): ModelsSettings {
 	const out: ModelsSettings = {};
 	for (const slot of MODEL_SLOTS) {
 		const cleaned = sanitizeRoleOverride(raw[slot]);
-		if (cleaned) out[slot] = cleaned;
+		if (cleaned) {
+			const value = raw[slot] as Record<string, unknown>;
+			out[slot] = {
+				...cleaned,
+				...(cleaned.model?.provider === "chatgpt" && typeof value.fastMode === "boolean" ? { fastMode: value.fastMode } : {}),
+			};
+		}
 	}
 	return out;
 }