fix(slack): one select instead of four rating buttons

Slack's mobile client gives every button in an actions block its own
full-width row, so the four ratings rendered as four stacked bars and the
nudge filled the screen (user, with a screenshot). A select is one row
and still one decision.

The interactive route now resolves both shapes — a button carries
`value`, a select carries it on `selected_option`. Reading only the
former would have left sharing working while rating silently did
nothing.

src/app/api/slack/interactive/route.ts

@@ -61,7 +61,12 @@ export async function POST(req: NextRequest) {
   if (payload.type !== "block_actions") return new NextResponse(null, { status: 200 });
 
   const action = payload.actions?.[0];
-  const [idStr, verb, arg] = String(action?.value ?? "").split(":");
+  // A button carries `value`; a select carries it on the chosen option. The
+  // ratings moved to a select because four buttons became four full-width rows
+  // on Slack mobile, so both shapes have to resolve or rating silently stops
+  // working while sharing still does.
+  const rawValue = action?.value ?? action?.selected_option?.value ?? "";
+  const [idStr, verb, arg] = String(rawValue).split(":");
   const transactionId = Number(idStr);
   if (!Number.isInteger(transactionId)) {
     return NextResponse.json({ text: "Could not tell which order that was." });