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/components/OmoFormFields.mergeCustomModelsIntoStore.test.ts

@@ -0,0 +1,111 @@
+import { describe, expect, it } from "vitest";
+import {
+  mergeCustomModelsIntoStore,
+  type CustomModelItem,
+} from "@/components/providers/forms/OmoFormFields";
+
+describe("mergeCustomModelsIntoStore", () => {
+  it("保留自定义项高级字段，并在模型变更时仅按需清理非法 variant", () => {
+    const store = {
+      sisyphus: { model: "builtin-model" },
+      "custom-agent": {
+        model: "model-a",
+        variant: "fast",
+        temperature: 0.2,
+        permission: { edit: "allow" },
+      },
+    };
+    const customs: CustomModelItem[] = [
+      { key: "custom-agent", model: "model-b", sourceKey: "custom-agent" },
+    ];
+
+    const merged = mergeCustomModelsIntoStore(
+      store,
+      new Set(["sisyphus"]),
+      customs,
+      { "model-b": ["precise"] },
+    );
+
+    expect(merged.sisyphus).toEqual({ model: "builtin-model" });
+    expect(merged["custom-agent"]).toEqual({
+      model: "model-b",
+      temperature: 0.2,
+      permission: { edit: "allow" },
+    });
+  });
+
+  it("重命名自定义 key 时迁移原有 variant 和高级字段", () => {
+    const store = {
+      sisyphus: { model: "builtin-model" },
+      "custom-agent-old": {
+        model: "model-a",
+        variant: "fast",
+        maxTokens: 8192,
+      },
+    };
+    const customs: CustomModelItem[] = [
+      {
+        key: "custom-agent-new",
+        sourceKey: "custom-agent-old",
+        model: "model-a",
+      },
+    ];
+
+    const merged = mergeCustomModelsIntoStore(
+      store,
+      new Set(["sisyphus"]),
+      customs,
+      { "model-a": ["fast", "balanced"] },
+    );
+
+    expect(merged["custom-agent-old"]).toBeUndefined();
+    expect(merged["custom-agent-new"]).toEqual({
+      model: "model-a",
+      variant: "fast",
+      maxTokens: 8192,
+    });
+  });
+
+  it("custom 列表为空时移除旧自定义项但保留内置项", () => {
+    const store = {
+      sisyphus: { model: "builtin-model" },
+      hephaestus: { model: "builtin-model-2" },
+      "custom-agent": { model: "model-a", temperature: 0.3 },
+    };
+
+    const merged = mergeCustomModelsIntoStore(
+      store,
+      new Set(["sisyphus", "hephaestus"]),
+      [],
+      {},
+    );
+
+    expect(merged).toEqual({
+      sisyphus: { model: "builtin-model" },
+      hephaestus: { model: "builtin-model-2" },
+    });
+  });
+
+  it("清空 model 时保留高级字段并移除 model/variant", () => {
+    const store = {
+      sisyphus: { model: "builtin-model" },
+      "custom-agent": {
+        model: "model-a",
+        variant: "fast",
+        temperature: 0.7,
+      },
+    };
+    const customs: CustomModelItem[] = [
+      { key: "custom-agent", model: "", sourceKey: "custom-agent" },
+    ];
+
+    const merged = mergeCustomModelsIntoStore(
+      store,
+      new Set(["sisyphus"]),
+      customs,
+      { "model-a": ["fast"] },
+    );
+
+    expect(merged["custom-agent"]).toEqual({ temperature: 0.7 });
+  });
+});