Fix session title input's border offset and width

The -mx-2 trick pushed the hover/focus border noticeably left of the
text, and flex-1 stretched the input across the whole header row.
Tighten the offset to px-1.5/-ml-1.5 and size the input to its content
via field-sizing:content instead.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WzyfRyA7h5rs5SCAahLAWd

app/(app)/sessions/[id]/page.tsx

@@ -36,7 +36,7 @@ export default async function SessionDetailPage({ params }: { params: Promise<{
       <div className="flex items-center justify-between gap-4">
         <div className="min-w-0 flex-1">
           <SessionTitleEditor sessionId={detail.session.id} initialName={detail.session.name} />
-          <p className="mt-1 px-2 text-sm text-muted-foreground">
+          <p className="mt-1 px-1.5 text-sm text-muted-foreground">
             {detail.session.status} · {formatDuration(detail.session.durationMs)}
             {detail.session.kind === "replay" && detail.replayedFromName !== undefined && (
               <> · replayed from {detail.replayedFromName ?? `session #${detail.session.replayedSessionId}`}</>
@@ -50,7 +50,7 @@ export default async function SessionDetailPage({ params }: { params: Promise<{
             )}
           </p>
           {detail.session.description && (
-            <p className="mt-1 px-2 text-sm text-muted-foreground">{detail.session.description}</p>
+            <p className="mt-1 px-1.5 text-sm text-muted-foreground">{detail.session.description}</p>
           )}
         </div>
         {canReplay && (