feat: Add retry mechanism for blocked tasks

Blocked tasks (from spawn failures) were a dead-end with no way to
recover. Add retryBlockedTask to DispatchManager that resets status
to pending and re-queues, a tRPC mutation that also kicks dispatchNext,
and a Retry button in the task slide-over when status is blocked.

apps/server/trpc/routers/dispatch.ts

@@ -35,5 +35,15 @@ export function dispatchProcedures(publicProcedure: ProcedureBuilder) {
         await dispatchManager.completeTask(input.taskId);
         return { success: true };
       }),
+
+    retryBlockedTask: publicProcedure
+      .input(z.object({ taskId: z.string().min(1) }))
+      .mutation(async ({ ctx, input }) => {
+        const dispatchManager = requireDispatchManager(ctx);
+        await dispatchManager.retryBlockedTask(input.taskId);
+        // Kick dispatch loop to pick up the re-queued task
+        await dispatchManager.dispatchNext();
+        return { success: true };
+      }),
   };
 }