Support form Assistant Streamdown (#46248)

Re-adds support form Assistant response using a lighter weight
Streamdown component vs the more heavy `Message` component.

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## Summary by CodeRabbit

* **New Features**
* AI Assistant follow-up card after ticket submission for project-scoped
requests.
* In-chat support request preview panels showing submitted subject and
message.

* **Improvements**
* Smarter project selection when opening the support form via
route/context.
* Success screen: cleaner layout, project-name messaging, optional
finish action, and a "Join Discord" button.
  * Category prompt text updated to "What issue are you having?"
  * New success/feedback section for consistent layouts.

* **Tests**
* Added tests covering support prompt serialization/parsing and UI
previews.

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apps/studio/components/ui/HelpPanel/HelpPanel.tsx

@@ -66,12 +66,7 @@ export const HelpPanel = ({
       </div>
       <div className="flex-1 overflow-hidden">
         {isSupportView ? (
-          <SupportForm
-            initialParams={supportLinkQueryParams}
-            onFinish={() => {
-              setView('home')
-            }}
-          />
+          <SupportForm initialParams={supportLinkQueryParams} />
         ) : (
           <div className="flex h-full flex-col overflow-y-auto pb-5">
             <HelpSection