feat(agents): expose thinking variant configuration in agent settings (#1715)

* feat(agents): expose thinking variant configuration in agent settings

Fix #1425: add variant field to agent config UI so users can configure
thinking/reasoning depth per agent without editing opencode.json.

Changes:
- Added variant to AgentConfig and AgentDraft types in useAgentsStore
- Pass variant in createAgent and updateAgent API calls
- Support null for temperature, top_p, and variant to clear overrides
- Added variant input field in AgentsPage 'Model & Parameters' section
- Added variant to settings search registry
- Added i18n strings for variant field in all 8 non-English locales

The variant field maps to provider-specific parameters (e.g. Anthropic
high/max variant, OpenAI reasoning effort). Users can enter any string
value; the SDK passes it through to the model provider.

Clearing temperature/topP/variant now sends null to the server instead
of omitting the field, which properly removes the override in
opencode.json.

* fix(sync): preserve tool state.time in materialization merge

* chore: trigger re-review

* fix(agents): use thinking variant selector in settings

* fix(agents): preserve thinking variant values

---------

Co-authored-by: Leonid Skorobogatyy <bash@opencode.itc.local>

packages/ui/src/lib/i18n/messages/ko.settings.ts

@@ -387,6 +387,10 @@ export const settingsDict = {
   'settings.agents.page.field.mode': '모드',
   'settings.agents.page.field.modeTooltip': '주 에이전트/보조 에이전트로 표시할지 선택합니다',
   'settings.agents.page.field.overrideModel': '모델 오버라이드',
+  'settings.agents.page.field.variant': '사고 변형',
+  'settings.agents.page.field.variantTooltip': '선택 사항. 모델이 추론을 지원하는 경우, 변형은 추론 깊이를 제어합니다.',
+  'settings.agents.page.field.variantHint': '모델별 (예: Anthropic variant)',
+  'settings.agents.page.field.variantPlaceholder': '예: high, max, low, none',
   'settings.agents.page.field.temperature': '온도',
   'settings.agents.page.field.temperatureTooltip': '무작위성을 제어합니다. 높을수록 창의적이고 낮을수록 집중적입니다.',
   'settings.agents.page.field.temperatureRange': '0.0 ~ 2.0',