test: update ultrabrain model expectations to gpt-5.4

The DEFAULT_CATEGORIES ultrabrain model was updated from openai/gpt-5.3-codex
to openai/gpt-5.4 in a previous commit, but test expectations were not updated.

Updated test expectations in:
- src/plugin-handlers/config-handler.test.ts (lines 560, 620)
- src/agents/utils.test.ts (lines 1119, 1232, 1234, 1301, 1303, 1316, 1318)

src/plugin-handlers/config-handler.test.ts

@@ -557,7 +557,7 @@ describe("Prometheus category config resolution", () => {
 
     // then
     expect(config).toBeDefined()
-    expect(config?.model).toBe("openai/gpt-5.3-codex")
+    expect(config?.model).toBe("openai/gpt-5.4")
     expect(config?.variant).toBe("xhigh")
   })
 
@@ -617,7 +617,7 @@ describe("Prometheus category config resolution", () => {
 
     // then - falls back to DEFAULT_CATEGORIES
     expect(config).toBeDefined()
-    expect(config?.model).toBe("openai/gpt-5.3-codex")
+    expect(config?.model).toBe("openai/gpt-5.4")
     expect(config?.variant).toBe("xhigh")
   })