Send reasoning content back to the model across turns via the reasoning_content API field (#21036)

* webui: send reasoning_content back to model in context

Preserve assistant reasoning across turns by extracting it from
internal tags and sending it as a separate reasoning_content field
in the API payload. The server and Jinja templates handle native
formatting (e.g. <think> tags for Qwen, GLM, DeepSeek...).

Adds "Exclude reasoning from context" toggle in Settings > Developer
(off by default, so reasoning is preserved). Includes unit tests.

* webui: add syncable parameter for excludeReasoningFromContext

* chore: update webui build output

tools/server/webui/src/lib/services/parameter-sync.service.ts

@@ -227,6 +227,12 @@ export const SYNCABLE_PARAMETERS: SyncableParameter[] = [
 		serverKey: 'alwaysShowAgenticTurns',
 		type: SyncableParameterType.BOOLEAN,
 		canSync: true
+	},
+	{
+		key: 'excludeReasoningFromContext',
+		serverKey: 'excludeReasoningFromContext',
+		type: SyncableParameterType.BOOLEAN,
+		canSync: true
 	}
 ];