feat(desktop): persistent needs-input indicator + icon button consolidation

Replace the background-clarify toast (expired on alt-tab, easy to miss) with a
persistent, glowing amber "needs input" dot on the session's sidebar row,
driven off a new ClientSessionState.needsInput flag mirrored into a
$attentionSessionIds store. The flag is set on clarify.request and cleared the
moment the turn resumes (tool.complete) or ends.

Also: redesign the clarify tool UI (borderless choices, pseudo-radio dots,
right-aligned checkmark, arc border, tighter padding), make Button the single
source of icon-button styling (4px radius, new icon-titlebar variant, titlebar
buttons rendered polymorphically via asChild, Codicons throughout), put the
file-tree refresh action first, and .trim() pasted composer text.

apps/desktop/src/app/chat/composer/index.tsx

@@ -407,13 +407,19 @@ export function ChatBar({
       return
     }
 
-    const pastedText = event.clipboardData.getData('text')
+    // Trim surrounding whitespace so a copy that dragged along leading/trailing
+    // blank lines (common when selecting from terminals, code blocks, web pages)
+    // doesn't dump multiline padding into the composer. Internal newlines are
+    // preserved — only the edges are cleaned up.
+    const pastedText = event.clipboardData.getData('text').trim()
 
     if (!pastedText) {
+      event.preventDefault()
+
       return
     }
 
-    if (DATA_IMAGE_URL_RE.test(pastedText.trim())) {
+    if (DATA_IMAGE_URL_RE.test(pastedText)) {
       event.preventDefault()
 
       return