MILAB-6848: list sc chains in classic annotation order

The chain mapping fix reordered the selector to Beta/Alpha and Delta/Gamma,
since array order is display order. Keep the producers' values and order the
labels Alpha/Beta and Gamma/Delta instead.

Author: mchernys

.changeset/fix-sc-tcr-chain-letters.md

@@ -3,4 +3,6 @@
 '@platforma-open/milaboratories.vj-usage': minor
 ---
 
-Fix single-cell TCR chain selector mapping: A/B were swapped for TCRAB and TCRGD. Producers (mixcr-clonotyping, import-vdj-data) assign A to the more diverse chains: Beta and Delta. The selector was running usage on the opposite chain from the one labelled. Existing blocks are relabelled only, with the stored chain value is unchanged, so nothing re-runs.
+Fix single-cell TCR chain selector mapping: A/B were swapped for TCRAB and TCRGD. Producers (mixcr-clonotyping, import-vdj-data) assign A to the more diverse chains: Beta and Delta. The selector was running usage on the opposite chain from the one labelled. Existing blocks are relabelled only, the stored chain value is unchanged, so nothing re-runs.
+
+The selector also lists chains in the classic annotation order again — Alpha/Beta and Gamma/Delta — instead of the value order A/B.

ui/src/utils.ts

@@ -32,8 +32,9 @@ export function useScChainOptions(
 
     const receptor = axisSpec.domain?.["pl7.app/vdj/receptor"];
 
+    // Values are the producers' (mixcr-clonotyping, import-vdj-data): A is the more diverse
+    // chain. Array order is display order, kept in the classic annotation order.
     let options: { label: string; value: string }[];
-    // A/B order is the producers' (mixcr-clonotyping, import-vdj-data): A is the more diverse chain.
     switch (receptor) {
       case "IG":
         options = [
@@ -43,14 +44,14 @@ export function useScChainOptions(
         break;
       case "TCRAB":
         options = [
-          { label: "Beta", value: "A" },
           { label: "Alpha", value: "B" },
+          { label: "Beta", value: "A" },
         ];
         break;
       case "TCRGD":
         options = [
-          { label: "Delta", value: "A" },
           { label: "Gamma", value: "B" },
+          { label: "Delta", value: "A" },
         ];
         break;
       default: