merge: sync challenge-6-stable-coin with base-challenge-template

Resolves recurring conflict from #355/#371/#374. Previous resolutions
were squash-merged, which never advanced the merge-base, so every
subsequent sync re-diffed from the same 11-commit-old point (a7fc831)
and reproduced the conflict. This is a real merge commit to fix that.

# Conflicts:
#	.github/workflows/main.yml
#	.github/workflows/sync_other_challenges.yaml
#	packages/snfoundry/contracts/Scarb.toml
#	packages/snfoundry/contracts/src/your_contract.cairo
#	packages/snfoundry/contracts/tests/test_contract.cairo

Author: tu11aa

.github/workflows/main.yml

@@ -18,6 +18,7 @@ on:
       - "yarn.lock"
       - "package.json"
       - ".tool-versions"
+      - ".github/workflows/**"
 
 permissions:
   contents: read

AGENTS.md

@@ -602,8 +602,8 @@ Also configure RPC URLs in `packages/nextjs/.env`:
 
 ```
 NEXT_PUBLIC_DEVNET_PROVIDER_URL=http://127.0.0.1:5050
-NEXT_PUBLIC_SEPOLIA_PROVIDER_URL=https://starknet-sepolia.public.blastapi.io/rpc/v0_9
-NEXT_PUBLIC_MAINNET_PROVIDER_URL=https://starknet-mainnet.public.blastapi.io/rpc/v0_9
+NEXT_PUBLIC_SEPOLIA_PROVIDER_URL=https://starknet-sepolia.g.alchemy.com/starknet/version/rpc/v0_10/_hKu4IgnPgrF8O82GLuYU
+NEXT_PUBLIC_MAINNET_PROVIDER_URL=https://starknet-mainnet.g.alchemy.com/starknet/version/rpc/v0_10/_hKu4IgnPgrF8O82GLuYU
 ```
 
 #### 3. Deploy your smart contract(s)

packages/nextjs/services/web3/websocket.ts

@@ -40,15 +40,15 @@ export const getWsUrlForChain = (chain: Chain): string => {
         sepoliaWs ||
         httpToWs(
           chain.rpcUrls.public.http[0] ||
-            "https://starknet-sepolia.public.blastapi.io/rpc/v0_9",
+            "https://starknet-sepolia.g.alchemy.com/starknet/version/rpc/v0_10/_hKu4IgnPgrF8O82GLuYU",
         )
       );
     case "mainnet":
       return (
         mainnetWs ||
         httpToWs(
           chain.rpcUrls.public.http[0] ||
-            "https://starknet-mainnet.public.blastapi.io/rpc/v0_9",
+            "https://starknet-mainnet.g.alchemy.com/starknet/version/rpc/v0_10/_hKu4IgnPgrF8O82GLuYU",
         )
       );
     default:

packages/nextjs/supportedChains.ts

@@ -28,7 +28,7 @@ const mainnetFork = {
       http: [rpcUrlDevnet],
     },
   },
-} as chains.Chain;
+} as const satisfies chains.Chain;
 
 const devnet = {
   ...chains.devnet,