Provide helper for resolving alias ID

[PaulRBerg]

From Claude's output in new-uI:

 Fix

 1. Create shared alias computation helper

 File: portal/lib/schema/stream-alias.ts (new)

 Helper that computes the stream alias from the contract address using the SDK:

 import { sablier } from "sablier";
 import { isEvmAddress } from "@/isomorphic/schema";

 export function computeStreamAlias(
   contract: string,
   chainId: number,
   tokenId: string,
   indexerAlias: string | null | undefined,
 ): string {
   // If the indexer provided a proper alias (not address-based), use it
   if (indexerAlias) {
     const source = indexerAlias.split("-")[0] ?? "";
     if (source && !isEvmAddress(source)) {
       return indexerAlias;
     }
   }

   // Compute alias from SDK
   const contractInfo = sablier.contracts.get({
     chainId,
     contractAddress: contract.toLowerCase(),
   });

   if (contractInfo?.alias) {
     return `${contractInfo.alias}-${chainId}-${tokenId}`;
   }

   // Fallback: address-based ID
   return `${contract.toLowerCase()}-${chainId}-${tokenId}`;
 }