fix(site): default the Streaming tab to added TTFT (asc), not streams-sustained

Streams sustained saturates at the harness cap (512), so it ties several
gateways and breaks the tie by name, floating a slow-TTFT gateway above a fast
one at the identical count (e.g. APISIX's 12,288us TTFT sorting above Busbar's
273us, both at 512). Added TTFT p99 is the streaming-overhead metric a user
feels first and it does not saturate, so it ranks the tab honestly. Passthrough
and Translation keep Sustained RPS @20ms (the cross-gateway comparison metric).

Author: MattJackson

site/app.js

@@ -37,7 +37,11 @@ const PERF_VIEWS = new Set(["passthrough", "translation", "streaming"]);
 const VIEW_ALIASES = { results: "passthrough", charts: "method" };
 // Each perf tab's default (and honest headline) sort column; a clean URL omits the sort when it
 // equals this, and switching tabs snaps to it unless the URL pins another.
-const VIEW_SORT = { passthrough: "rps20", translation: "xlrps", streaming: "streams" };
+// Streaming defaults to added TTFT (asc), NOT streams-sustained: the sustained count saturates at the
+// harness cap (512) so it ties several gateways and breaks ties by name, floating a slow-TTFT gateway
+// above a fast one at the same count. Added TTFT is the streaming-overhead discriminator that a user
+// actually feels first and it does not saturate.
+const VIEW_SORT = { passthrough: "rps20", translation: "xlrps", streaming: "sttft" };
 
 /* Language chip colours: kept in sync with LANG_COLORS in charts.py. */
 const LANG_COLORS = {