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/components/sections/agents/AgentsSidebar.tsx

@@ -232,6 +232,7 @@ export const AgentsSidebar: React.FC<AgentsSidebarProps> = ({ onItemSelect }) =>
       scope: extAgent.scope || 'user',
       description: agent.description,
       model: modelStr,
+      variant: agent.variant,
       temperature: agent.temperature,
       top_p: agent.topP,
       prompt: agent.prompt,
@@ -277,6 +278,7 @@ export const AgentsSidebar: React.FC<AgentsSidebarProps> = ({ onItemSelect }) =>
       name: sanitizedName,
       description: renameDialogAgent.description,
       model: renameModelStr,
+      variant: renameDialogAgent.variant,
       temperature: renameDialogAgent.temperature,
       top_p: renameDialogAgent.topP,
       prompt: renameDialogAgent.prompt,