fix(stubmerger): 依赖 stub/text 为空误杀恢复静默跳过

stdio.vp 等纯声明模块（全 pass）text.ll 为空是合法形态，stub.ll
为空同理（纯常量/纯导入模块）。fail-fast 改造对"文件存在但为空"
加了错误上报导致误杀，恢复静默跳过；文件缺失分支保留 fail-fast。

App/lib/core/StubMerger.vp

@@ -968,11 +968,8 @@ def _LoadAndAppendStub(temp_dir: str, td_len: t.CSizeT, dep_sha1: str,
     df_ls.close()
     stdlib.free(dep_path)
     if dep_br_ls <= 0:
-        if LookupSha1RelPath(dep_sha1) is not None:
-            fb_ls2: str = VLogger.fmt_buf()
-            if fb_ls2 is not None:
-                viperlib.snprintf(fb_ls2, 1024, "依赖 stub 为空: %s", dep_sha1)
-                VLogger.error(fb_ls2, "StubMerger")
+        # 依赖 stub 为空：纯声明/纯常量模块（如 stdio.vp 全 pass、CDefine 模块）
+        # 无可声明符号，stub.ll 为空属合法形态，静默跳过
         return out_pos
     if dep_br_ls < STUB_READ_BUF_SIZE:
         dep_buf[dep_br_ls] = '\0'
@@ -1138,11 +1135,8 @@ def _LoadAndAppendTextDeclares(temp_dir: str, td_len: t.CSizeT, dep_sha1: str,
     tf_lt.close()
     stdlib.free(text_path)
     if text_br <= 0:
-        if LookupSha1RelPath(dep_sha1) is not None:
-            fb_lt2: str = VLogger.fmt_buf()
-            if fb_lt2 is not None:
-                viperlib.snprintf(fb_lt2, 1024, "依赖 text 为空: %s", dep_sha1)
-                VLogger.error(fb_lt2, "StubMerger")
+        # 依赖 text 为空：纯 stub 模块（如 stdio.vp 全 pass 声明）无函数体，
+        # text.ll 为空属合法形态，无可提取 declare，静默跳过
         return out_pos
     if text_br < STUB_READ_BUF_SIZE:
         dep_buf[text_br] = '\0'