fix(delegate-task): reject stray backend-style categories

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/agents/prometheus-gpt-category-prompt.test.ts

@@ -0,0 +1,14 @@
+declare const require: (name: string) => any
+const { describe, expect, test } = require("bun:test")
+import { PROMETHEUS_GPT_SYSTEM_PROMPT } from "./prometheus/gpt"
+
+describe("PROMETHEUS_GPT_SYSTEM_PROMPT category guidance", () => {
+	test("#given recommended agent profile instructions #when reading category placeholder #then it must point planners at available categories rather than a free-form name", () => {
+		//#given
+		const prompt = PROMETHEUS_GPT_SYSTEM_PROMPT
+
+		//#when / #then
+		expect(prompt).not.toContain("Category: `[name]`")
+		expect(prompt).toContain("Category: `[category-from-available-categories-above]`")
+	})
+})