fix(agents): deny apply_patch for GPT models to prevent verification hangs (#2935)

GPT models (5.3-codex, 5.4, etc.) frequently hang when using apply_patch
due to verification loops. This adds:

1. Tool restriction: apply_patch is denied for GPT variants of
   Hephaestus, Sisyphus-Junior, and Sisyphus agents
2. Prompt guidance: GPT-specific prompts now explicitly instruct using
   edit/write tools instead of apply_patch
3. Removed the 'Always use apply_patch' instruction from
   sisyphus-junior/gpt-5-4.ts that contradicted the fix

The deny is model-conditional — Claude variants retain apply_patch
access since it works reliably there.

src/agents/hephaestus/agent.ts

@@ -1,6 +1,6 @@
 import type { AgentConfig } from "@opencode-ai/sdk";
 import type { AgentMode, AgentPromptMetadata } from "../types";
-import { isGpt5_4Model, isGpt5_3CodexModel } from "../types";
+import { isGptModel, isGpt5_4Model, isGpt5_3CodexModel } from "../types";
 import type {
   AvailableAgent,
   AvailableTool,
@@ -120,6 +120,7 @@ export function createHephaestusAgent(
     permission: {
       question: "allow",
       call_omo_agent: "deny",
+      ...(isGptModel(model) ? { apply_patch: "deny" as const } : {}),
     } as AgentConfig["permission"],
     reasoningEffort: "medium",
   };