fix(wechat): deliver failure notices and hot-swappable wechat-mp bundle

Notify users when HTML publish guards reject stub pages instead of silently
failing, send real page links when non-stub files exist, and split wechat-mp
into wechat-mp.bundle.mjs for fast production updates without full portal rebuilds.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/release-portal-runtime-prod.sh

@@ -151,7 +151,7 @@ fi
 
 verify_runtime_artifact() {
   local missing=0
-  for required in server.mjs mindspace-sandbox-mcp.mjs mindspace-public-links.mjs dist package.json scripts/run-memind-portal-prod.sh scripts/check-mindspace-public-links.mjs scripts/load-env.mjs scripts/wechat-mp-menu.mjs scripts/memind-portal-tunnel.sh; do
+  for required in server.mjs wechat-mp.bundle.mjs mindspace-sandbox-mcp.mjs mindspace-public-links.mjs dist package.json scripts/run-memind-portal-prod.sh scripts/check-mindspace-public-links.mjs scripts/load-env.mjs scripts/wechat-mp-menu.mjs scripts/memind-portal-tunnel.sh; do
     if [[ ! -e "${RUNTIME_ROOT}/${required}" ]]; then
       echo "runtime 产物缺失: ${RUNTIME_ROOT}/${required}" >&2
       missing=1