feat(omo): improve agent model selection UX and fix lowercase keys (#1004)

* fix(omo): use lowercase keys for builtin agent definitions

OMO config schema expects all agent keys to be lowercase.
Updated OMO_BUILTIN_AGENTS keys (Sisyphus → sisyphus, Hephaestus →
hephaestus, etc.) and aligned Rust test fixtures accordingly.

* feat(omo): add i18n support and tooltips for agent/category descriptions

* feat(omo): add preset model variants for thinking level support

Add OPENCODE_PRESET_MODEL_VARIANTS constant with variant definitions
for Google, OpenAI, and Anthropic models. The omoModelVariantsMap
builder now falls back to presets when config-defined variants are
absent, enabling the variant selector for supported models.

* feat(omo): replace model select with searchable combobox and improve fallback handling

* feat(omo): enrich preset model defaults and metadata fallback

* fix(omo): preserve custom fields and align otherFields import/validation

* fix: resolve omo clippy warnings and include app update

tests/utils/omoConfig.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from "vitest";
+import {
+  mergeOmoConfigPreview,
+  parseOmoOtherFieldsObject,
+  type OmoGlobalConfig,
+} from "@/types/omo";
+
+const EMPTY_GLOBAL: OmoGlobalConfig = {
+  id: "global",
+  disabledAgents: [],
+  disabledMcps: [],
+  disabledHooks: [],
+  disabledSkills: [],
+  updatedAt: "2026-01-01T00:00:00.000Z",
+};
+
+describe("parseOmoOtherFieldsObject", () => {
+  it("解析对象 JSON", () => {
+    expect(parseOmoOtherFieldsObject('{ "foo": 1 }')).toEqual({ foo: 1 });
+  });
+
+  it("数组/字符串返回 undefined", () => {
+    expect(parseOmoOtherFieldsObject('["a"]')).toBeUndefined();
+    expect(parseOmoOtherFieldsObject('"hello"')).toBeUndefined();
+  });
+
+  it("非法 JSON 抛出异常", () => {
+    expect(() => parseOmoOtherFieldsObject("{")).toThrow();
+  });
+});
+
+describe("mergeOmoConfigPreview", () => {
+  it("只合并 otherFields 的对象值，忽略数组", () => {
+    const mergedFromArray = mergeOmoConfigPreview(
+      EMPTY_GLOBAL,
+      {},
+      {},
+      '["a", "b"]',
+    );
+    expect(mergedFromArray).toEqual({});
+
+    const mergedFromObject = mergeOmoConfigPreview(
+      EMPTY_GLOBAL,
+      {},
+      {},
+      '{ "foo": "bar" }',
+    );
+    expect(mergedFromObject).toEqual({ foo: "bar" });
+  });
+});