refactor: replace the legacy function runtime with shared

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/syntax/src/v060.ts

@@ -1,6 +1,6 @@
 import { Lexer, LexError } from "./tokenizer.ts";
 
-export type FunctionRuntime = "legacy" | "client" | "server" | "shared";
+export type FunctionRuntime = "client" | "server" | "shared";
 export type StateRuntime = "shared" | "client" | "server";
 export type StoreKind = "global" | "page";
 
@@ -206,7 +206,7 @@ export function parseRuntimeFunctions(source: string): RuntimeFunctionDecl[] {
       i++;
       continue;
     }
-    let runtime: FunctionRuntime = "legacy";
+    let runtime: FunctionRuntime = "shared";
     if (["client", "server", "shared"].includes(token.word)) {
       runtime = token.word as FunctionRuntime;
       i = skipTrivia(source, token.end);