chore: remove unused isMinimal param from buildSkillsSection

Address review feedback: isMinimal is no longer referenced after the
early-return guard was removed in the parent commit.

(cherry picked from commit 2efe04d301)

src/agents/system-prompt.ts

@@ -17,11 +17,7 @@ import { sanitizeForPromptLiteral } from "./sanitize-for-prompt.js";
 export type PromptMode = "full" | "minimal" | "none";
 type OwnerIdDisplay = "raw" | "hash";
 
-function buildSkillsSection(params: {
-  skillsPrompt?: string;
-  isMinimal: boolean;
-  readToolName: string;
-}) {
+function buildSkillsSection(params: { skillsPrompt?: string; readToolName: string }) {
   const trimmed = params.skillsPrompt?.trim();
   if (!trimmed) {
     return [];
@@ -392,7 +388,6 @@ export function buildAgentSystemPrompt(params: {
   ];
   const skillsSection = buildSkillsSection({
     skillsPrompt,
-    isMinimal,
     readToolName,
   });
   const memorySection = buildMemorySection({