fix(model-requirements): use supported variant for gemini-3-pro (#1463)

* fix(model-requirements): use supported variant for gemini-3-pro

* fix(delegate-task): update artistry variant to high for gemini-3-pro

- Update DEFAULT_CATEGORIES artistry variant from 'max' to 'high'
- Update related test comment
- gemini-3-pro only supports low/high thinking levels, not max
- Addresses Oracle review feedback

src/shared/model-requirements.test.ts

@@ -313,7 +313,7 @@ describe("CATEGORY_MODEL_REQUIREMENTS", () => {
 
     const primary = artistry.fallbackChain[0]
     expect(primary.model).toBe("gemini-3-pro")
-    expect(primary.variant).toBe("max")
+    expect(primary.variant).toBe("high")
     expect(primary.providers[0]).toBe("google")
   })