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/stores/chat.svelte.ts

@@ -1479,6 +1479,8 @@ class ChatStore {
 
 		if (currentConfig.disableReasoningParsing) apiOptions.disableReasoningParsing = true;
 
+		if (currentConfig.excludeReasoningFromContext) apiOptions.excludeReasoningFromContext = true;
+
 		if (hasValue(currentConfig.temperature))
 			apiOptions.temperature = Number(currentConfig.temperature);