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/pl.settings.ts

@@ -28,6 +28,10 @@ export const settingsDict = {
   'settings.agents.page.field.overrideModel': 'Nadpisz model',
   'settings.agents.page.field.scopePlaceholder': 'Zakres',
   'settings.agents.page.field.systemPromptPlaceholder': 'Jesteś ekspertem w asystowaniu przy kodowaniu...',
+  'settings.agents.page.field.variant': 'Wariant myślenia',
+  'settings.agents.page.field.variantTooltip': 'Opcjonalne. Jeśli model obsługuje rozumowanie, wariant kontroluje głębokość rozumowania.',
+  'settings.agents.page.field.variantHint': 'Zależne od modelu (np. wariant Anthropic)',
+  'settings.agents.page.field.variantPlaceholder': 'np. high, max, low, none',
   'settings.agents.page.field.temperature': 'Temperatura',
   'settings.agents.page.field.temperatureRange': 'od 0.0 do 2.0',
   'settings.agents.page.field.temperatureTooltip': 'Kontroluje losowość. Wyższa = bardziej kreatywny, niższa = bardziej skupiony.',