fix: queryToSql dropped OFFSET 0 due to falsy check

Same class of bug as the LIMIT 0 fix — `if (query.offset)` treated
offset=0 as falsy and omitted the OFFSET clause from generated SQL.
Changed to `if (query.offset !== undefined)`. Added tests for both
LIMIT 0 and OFFSET 0 preservation.

Author: teamchong

src/wasm-engine.integration.test.ts

@@ -388,4 +388,14 @@ describe("queryToSql", () => {
     const sql = queryToSql({ ...base, filters: [{ column: "x", op: "not_between", value: [10, 20] }] });
     expect(sql).toContain("NOT BETWEEN 10 AND 20");
   });
+
+  it("preserves LIMIT 0", () => {
+    const sql = queryToSql({ ...base, limit: 0 });
+    expect(sql).toContain("LIMIT 0");
+  });
+
+  it("preserves OFFSET 0", () => {
+    const sql = queryToSql({ ...base, offset: 0 });
+    expect(sql).toContain("OFFSET 0");
+  });
 });

src/wasm-engine.ts

@@ -1077,7 +1077,7 @@ export function queryToSql(query: QueryDescriptor): string {
   if (query.groupBy?.length) parts.push(`GROUP BY ${query.groupBy.map(quote).join(", ")}`);
   if (query.sortColumn) parts.push(`ORDER BY ${quote(query.sortColumn)} ${query.sortDirection?.toUpperCase() ?? "ASC"}`);
   if (query.limit !== undefined) parts.push(`LIMIT ${query.limit}`);
-  if (query.offset) parts.push(`OFFSET ${query.offset}`);
+  if (query.offset !== undefined) parts.push(`OFFSET ${query.offset}`);
 
   return parts.join(" ");
 }