perf(ui): split right panel and secondary viewer chunks (#239)

## Summary
- split the right panel, picker, and tool call secondary viewers into
smaller deferred chunks
- release hidden right-panel file buffers and stop tracking static
tool-call scrollers when they are not needed
- keep this branch focused on the remaining secondary viewer chunking
work now that the Monaco-specific chunking moved into PR 215

## Testing
- npm run build --workspace @codenomad/ui

packages/ui/src/components/message-part.tsx

@@ -1,5 +1,4 @@
-import { Show, Match, Switch } from "solid-js"
-import ToolCall from "./tool-call"
+import { Match, Show, Suspense, Switch, lazy } from "solid-js"
 import { isItemExpanded, toggleItemExpanded } from "../stores/tool-call-state"
 import { Markdown } from "./markdown"
 import { useTheme } from "../lib/theme"
@@ -7,6 +6,8 @@ import { partHasRenderableText, SDKPart, TextPart, ClientPart } from "../types/m
 
 type ToolCallPart = Extract<ClientPart, { type: "tool" }>
 
+const LazyToolCall = lazy(() => import("./tool-call"))
+
 interface MessagePartProps {
   part: ClientPart
   messageType?: "user" | "assistant"
@@ -153,12 +154,14 @@ export default function MessagePart(props: MessagePartProps) {
       </Match>
 
       <Match when={partType() === "tool"}>
-        <ToolCall
-          toolCall={props.part as ToolCallPart}
-          toolCallId={props.part?.id}
-          instanceId={props.instanceId}
-          sessionId={props.sessionId}
-        />
+        <Suspense fallback={<div class="tool-call tool-call-loading" />}>
+          <LazyToolCall
+            toolCall={props.part as ToolCallPart}
+            toolCallId={props.part?.id}
+            instanceId={props.instanceId}
+            sessionId={props.sessionId}
+          />
+        </Suspense>
       </Match>