log why the frame fetch failed

'gitea unreachable' on its own is not a diagnosis. The sidecar was answering
200 to a direct curl while the panel showed that message, which sent the search
to the wrong half of the system twice.

api/router.ts

@@ -98,7 +98,10 @@ router_.all('/_web/*', async (ctx) => {
       redirect: 'manual',
     });
     return new Response(upstream.body, { status: upstream.status, headers: upstream.headers });
-  } catch {
+  } catch (err) {
+    // Logged, not swallowed. "unreachable" on its own sent two people to the wrong half of the system:
+    // the sidecar was answering 200 to a direct curl the whole time, and the failure was here.
+    console.error(`[gitea] frame ${method} ${subpath} -> ${sidecar} failed:`, err);
     return ctx.text('gitea unreachable', 502);
   }
 });