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

package.json

@@ -57,6 +57,7 @@
     "@radix-ui/react-dialog": "^1.1.15",
     "@radix-ui/react-dropdown-menu": "^2.1.16",
     "@radix-ui/react-label": "^2.1.7",
+    "@radix-ui/react-popover": "^1.1.15",
     "@radix-ui/react-scroll-area": "^1.2.10",
     "@radix-ui/react-select": "^2.2.6",
     "@radix-ui/react-slot": "^1.2.3",