Reopen rounds, file type buttons, checklist live-update

- Add reopenRound() to round engine (CLOSED → ACTIVE) with auto-pause of subsequent active rounds
- Add reopen endpoint to roundEngine router and UI button on round detail page
- Replace free-text MIME type input with toggle-only badge buttons in file requirements editor
- Enable refetchOnWindowFocus and shorter polling intervals for readiness checklist queries

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

src/server/routers/roundEngine.ts

@@ -5,6 +5,7 @@ import {
   activateRound,
   closeRound,
   archiveRound,
+  reopenRound,
   transitionProject,
   batchTransitionProjects,
   getProjectRoundStates,
@@ -53,6 +54,23 @@ export const roundEngineRouter = router({
       return result
     }),
 
+  /**
+   * Reopen a round: ROUND_CLOSED → ROUND_ACTIVE
+   * Pauses any subsequent active rounds in the same competition.
+   */
+  reopen: adminProcedure
+    .input(z.object({ roundId: z.string() }))
+    .mutation(async ({ ctx, input }) => {
+      const result = await reopenRound(input.roundId, ctx.user.id, ctx.prisma)
+      if (!result.success) {
+        throw new TRPCError({
+          code: 'BAD_REQUEST',
+          message: result.errors?.join('; ') ?? 'Failed to reopen round',
+        })
+      }
+      return result
+    }),
+
   /**
    * Archive a round: ROUND_CLOSED → ROUND_ARCHIVED
    */