M2: Wire frontend to mainnet — env-driven network and contract address

- CONTRACT_ADDRESS reads from NEXT_PUBLIC_CONTRACT_ADDRESS env var
- Default network switches to mainnet (was hardcoded testnet)
- Explorer links no longer hardcode chain=testnet
- .env.local (testnet) and .env.production (mainnet) templates added
- Both files gitignored to protect future secrets
- Frontend builds clean (verified)

Author: Glory Matthew

web/.gitignore

@@ -1 +1,6 @@
 .vercel
+.next/
+node_modules/
+.env.local
+.env.production
+.env.*.local

web/src/components/flash-loan/FlashLoanForm.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useState, useEffect } from "react";
+import { useState } from "react";
 import { useStacks } from "@/lib/hooks/useStacks";
 import { useFlashLoan } from "@/lib/hooks/useFlashLoan";
 import { useProtocolStats } from "@/lib/hooks/useProtocolStats";
@@ -158,7 +158,7 @@ export function FlashLoanForm() {
             <p className="text-green-400 text-sm font-medium">Transaction submitted</p>
             {txId && (
               <a
-                href={`https://explorer.hiro.so/txid/${txId}?chain=testnet`}
+                href={`https://explorer.hiro.so/txid/${txId}`}
                 target="_blank"
                 rel="noopener noreferrer"
                 className="text-green-400/80 text-xs underline mt-1 block"

web/src/lib/providers/StacksProvider.tsx

@@ -23,7 +23,9 @@ const StacksContext = createContext<StacksContextValue | null>(null);
 export function StacksProvider({ children }: { children: React.ReactNode }) {
   const [isWalletConnected, setIsWalletConnected] = useState(false);
   const [stxAddress, setStxAddress] = useState<string | null>(null);
-  const [network, setNetwork] = useState<NetworkType>("testnet");
+  const [network, setNetwork] = useState<NetworkType>(
+    (process.env.NEXT_PUBLIC_NETWORK as NetworkType) ?? "mainnet"
+  );
 
   const hydrateFromStorage = useCallback(() => {
     if (typeof window === "undefined") return;

web/src/lib/stacks/config.ts

@@ -2,7 +2,8 @@ import { STACKS_TESTNET, STACKS_MAINNET, StacksNetwork } from "@stacks/network";
 
 export type NetworkType = "testnet" | "mainnet";
 
-export const CONTRACT_ADDRESS = "ST3JAZD8CJ9XX3WNN2G61C7HD4RY333MRKPR5JGW7";
+// Mainnet deployer address — update after mainnet deployment
+export const CONTRACT_ADDRESS = process.env.NEXT_PUBLIC_CONTRACT_ADDRESS ?? "SP3JAZD8CJ9XX3WNN2G61C7HD4RY333MRKPR5JGW7";
 export const CONTRACT_NAME = "flashstack-core";
 
 export const RECEIVER_CONTRACTS = [