feat: remove supported-platforms feature gate (#2335)

## Summary

This PR removes the `supported-platforms` feature flag, enabling all
network platforms by default in the wallet selection drawer.

## Changes

###
`packages/keychain/src/components/purchasenew/checkout/onchain/wallet-drawer.tsx`
- Removed the `isSupportedPlatformsEnabled` feature flag hook call
- Updated `selectedNetworks` useMemo to always include all platforms:
starknet, ethereum, base, arbitrum, and optimism
- Removed `isSupportedPlatformsEnabled` from the dependency array
- Minor formatting improvements

### `packages/keychain/src/hooks/features.tsx`
- Removed `supported-platforms` from the `Feature` type union

## Result

All network platforms are now always available in the wallet selection
drawer without requiring feature flag enablement.

Author: broody

packages/keychain/src/components/purchasenew/checkout/onchain/wallet-drawer.tsx

@@ -31,7 +31,6 @@ export function WalletSelectionDrawer({
   isOpen,
   onClose,
 }: WalletSelectionDrawerProps) {
-  const isSupportedPlatformsEnabled = useFeature("supported-platforms");
   const isApplePayEnabled = useFeature("apple-pay-support");
 
   const { isMainnet, externalDetectWallets } = useConnection();
@@ -52,17 +51,15 @@ export function WalletSelectionDrawer({
   >(new Map());
 
   const selectedNetworks = useMemo(() => {
-    const platforms = isSupportedPlatformsEnabled
-      ? "starknet;ethereum;base;arbitrum;optimism"
-      : "starknet";
-
-    let networks =
-      platforms
-        ?.split(";")
-        .map((platform) =>
-          networkWalletData.networks.find((n) => n.platform === platform),
-        )
-        .filter(Boolean) || [];
+    const platforms = isMainnet
+      ? ["starknet", "ethereum", "base", "arbitrum", "optimism"]
+      : ["starknet"];
+
+    let networks = platforms
+      .map((platform) =>
+        networkWalletData.networks.find((n) => n.platform === platform),
+      )
+      .filter(Boolean);
 
     // If acquisition type is claimed, filter networks to only show those with merkle drop support
     if (starterpackDetails?.type === "claimed") {
@@ -78,7 +75,7 @@ export function WalletSelectionDrawer({
     }
 
     return networks as Network[];
-  }, [starterpackDetails, isSupportedPlatformsEnabled]);
+  }, [isMainnet, starterpackDetails]);
 
   // Reset state when drawer closes
   useEffect(() => {

packages/keychain/src/hooks/features.tsx

@@ -10,11 +10,7 @@ import React, {
 
 const LOCAL_STORAGE_KEY = "@cartridge/features";
 
-export type Feature =
-  | "none"
-  | "connections"
-  | "supported-platforms"
-  | "apple-pay-support";
+export type Feature = "none" | "connections" | "apple-pay-support";
 
 // --- Helper Functions ---