chore: update conventions to explicitly ban TypeScript enum

Convention #3 already said to use `as const` arrays, but didn't
explicitly call out TypeScript `enum` as bad. Enums cause type cast
issues when crossing WASM/serde boundaries. Added enum to the "Bad"
examples and added WASM/serde reasoning to "Why".

BTC-3226

Author: lcovar

CONVENTIONS.md

@@ -104,13 +104,17 @@ const total = parseInt(amount) + parseInt(fee); // ❌ Loses precision
 - IDE autocomplete
 - Exhaustiveness checking in switch statements
 - Less repetitive than `enum` (no `Key = "Key"` duplication)
+- TypeScript `enum` values cause type cast issues when crossing WASM/serde boundaries. The `as const` pattern avoids this entirely.
 
 **Good:**
 
 ```typescript
 export const TransactionType = ["Send", "StakingActivate", "StakingDeactivate"] as const;
 export type TransactionType = (typeof TransactionType)[number];
 
+export const TonStakingType = ["TonWhales", "SingleNominator", "MultiNominator"] as const;
+export type TonStakingType = (typeof TonStakingType)[number];
+
 function handleTx(type: TransactionType) {
   switch (type) {
     case "Send":
@@ -125,11 +129,16 @@ function handleTx(type: TransactionType) {
 **Bad:**
 
 ```typescript
+// ❌ TypeScript enum — causes type cast issues across WASM boundaries
+enum TransactionType {
+  Send = "Send",
+  StakingActivate = "StakingActivate",
+}
+
 // ❌ No type safety, typos not caught
 function handleTx(type: string) {
   if (type === "send") {
     // Oops, wrong case
-    // ...
   }
 }