fix(sidebar): remove flex-1 stretch on repos section; move quality tip inside

- flex:1 on repos section was expanding it to fill all sidebar height,
creating a large empty gap below the repo list
- ContextualTip was a sibling rendered outside the section — moved inside
so it's visually grouped with the repo list
- Adjusted .ctip padding to match section context

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/components/Sidebar.jsx

@@ -407,7 +407,7 @@ export default function Sidebar({ repos, reposLoading, activeRepo, onSelectRepo,
       )}
 
       {/* ── Repos ── */}
-      <div className="sidebar-section" style={{ flex: 1 }}>
+      <div className="sidebar-section">
         <div className="section-label">Indexed Repos ({reposLoading ? "…" : repos.length})</div>
         {reposLoading ? (
           // Skeleton while the first fetch is in flight — backend can take a moment on cold start
@@ -498,11 +498,9 @@ export default function Sidebar({ repos, reposLoading, activeRepo, onSelectRepo,
             })}
           </div>
         )}
+        {repos.length > 0 && <ContextualTip />}
       </div>
 
-      {/* ── Quality tip ── */}
-      {repos.length > 0 && <ContextualTip />}
-
       {/* ── Recent chats ── */}
       {sessions && sessions.length > 0 && (
         <div className="sidebar-section">

ui/src/index.css

@@ -1531,9 +1531,9 @@ textarea:focus-visible {
   color: var(--text);
 }
 
-/* ── Contextual retrieval tip — collapsible, low-key ── */
+/* ── Contextual retrieval tip — sits inside the repos section ── */
 .ctip {
-  padding: 0 16px 14px;
+  padding: 6px 0 2px;
 }
 .ctip-trigger {
   display: flex;