fix(syntax): reject bare apis-container bodies and cross-mode duplicate api names

Bare bodies inside apis {} silently discarded their text with no error,
producing a do-nothing block. They now throw a ParseError naming the entry
and pointing at the response {} section. Duplicate-name detection for
dataApis moved from an incremental, order-dependent check (only saw prior
entries in the array) to a single post-parse pass over the whole ast.dataApis,
so it catches cross-mode duplicates (apis {} vs ssr { api }) regardless of
declaration order.

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

packages/syntax/src/parser.ts

@@ -853,12 +853,7 @@ export function parse(source: string): PageAst {
         case "apis": {
           lx.next();
           const body = lx.readBalancedBraces();
-          for (const entry of parseApiEntries(body)) {
-            if (dataApis.some((block) => block.name === entry.name)) {
-              throw new ParseError(`Duplicate api entry "${entry.name}" in apis block`);
-            }
-            dataApis.push(entry);
-          }
+          dataApis.push(...parseApiEntries(body));
           break;
         }
         default:
@@ -951,6 +946,15 @@ export function parse(source: string): PageAst {
       visited.add(name);
     };
     for (const name of namedLoads.keys()) visitLoad(name);
+
+    const seenApiNames = new Set<string>();
+    for (const block of dataApis) {
+      if (seenApiNames.has(block.name)) {
+        throw new ParseError(`Duplicate api entry "${block.name}"`, "WRN-API-DUPLICATE");
+      }
+      seenApiNames.add(block.name);
+    }
+
     return {
       type: "page",
       imports,