feat(ncm): 网易云技术栈预研+构建验证 (agent-200) — 选型: mbedtls3.6.2裁剪(TLS+AES+MD5+RSA raw+Base64,~388KB)/jsmn(2.2KB)/qrcodegen(10.8KB)/minimp3(37.4KB), 合计~438KB; HTTPS unikey 全链路宿主+qemu-mipsel 实测通过; RSA raw 与 Python pow 逐字节一致; MP3 解码非瓶颈

vendor源码+out产物不入库(126MB, gitignore; 版本/许可/裁剪见 VENDOR_NOTES.md, build_*.sh 可复现)

patch_v2/ncm_app/build_dr_mp3.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+# dr_mp3 — 单文件 header（dr_mp3.h）。许可 MIT/public domain (双许可)。较重但兼容性/质量更好。
+. ./libs_common.sh
+D="$OUT/dr_mp3/mipsel"; mkdir -p "$D"
+cat > "$D/dr_mp3_impl.c" <<'C'
+#define DR_MP3_IMPLEMENTATION
+#include "dr_mp3.h"
+C
+$CC_MIPS -Os -I"$VENDOR/dr_mp3" -fno-stack-protector -ffunction-sections -fdata-sections -c "$D/dr_mp3_impl.c" -o "$D/dr_mp3.o" || exit 1
+$AR_MIPS rcs "$D/libdr_mp3.a" "$D/dr_mp3.o"
+echo "dr_mp3 (mipsel):"
+measure_archive "$D/libdr_mp3.a"