fix: 修复 http 纯静态部署下本地账号登录不可用（issue #131）

- user_store.js：crypto.subtle 仅安全上下文可用，http://:8090 下为 undefined
  导致播种/校验静默失败；新增纯 JS SHA-256 降级实现（已对照 Node crypto
  验证一致，含非 ASCII），WebCrypto 可用时仍优先
- session.js：/auth/login 返回 5xx/非 JSON 时判定为后端不可用并降级本地
  账号，仅 4xx 视为真实鉴权失败（原逻辑把 nginx 500 HTML 误判为密码错误）

web/auth/user_store.js

@@ -29,12 +29,71 @@ var UserStore = (function () {
     crypto.getRandomValues(buf);
     return Array.from(buf).map(function (b) { return b.toString(16).padStart(2, "0"); }).join("");
   }
+  /* 纯 JS SHA-256（geraintluff 实现，公有领域）：crypto.subtle 仅在
+   * 安全上下文（https / localhost）可用，纯静态 http 部署（如 :8090）
+   * 必须降级到此实现，否则本地账号无法播种/校验。 */
+  function sha256Js(ascii) {
+    function rr(v, a) { return (v >>> a) | (v << (32 - a)); }
+    var mp = Math.pow, mw = mp(2, 32), result = "", words = [];
+    var bitLen = ascii.length * 8;
+    var hash = (sha256Js.h = sha256Js.h || []);
+    var k = (sha256Js.k = sha256Js.k || []);
+    var pc = k.length, comp = {};
+    for (var c = 2; pc < 64; c++) {
+      if (!comp[c]) {
+        for (var i = 0; i < 313; i += c) comp[i] = c;
+        hash[pc] = (mp(c, 0.5) * mw) | 0;
+        k[pc++] = (mp(c, 1 / 3) * mw) | 0;
+      }
+    }
+    ascii += "\x80";
+    while ((ascii.length % 64) - 56) ascii += "\x00";
+    for (var i = 0; i < ascii.length; i++) {
+      var j = ascii.charCodeAt(i);
+      if (j >> 8) throw new Error("sha256Js: 仅接受字节串");
+      words[i >> 2] |= j << (((3 - i) % 4) * 8);
+    }
+    words[words.length] = (bitLen / mw) | 0;
+    words[words.length] = bitLen;
+    for (var j = 0; j < words.length;) {
+      var w = words.slice(j, (j += 16));
+      var old = hash;
+      hash = hash.slice(0, 8);
+      for (var i = 0; i < 64; i++) {
+        var w15 = w[i - 15], w2 = w[i - 2];
+        var a = hash[0], e = hash[4];
+        var t1 = hash[7] + (rr(e, 6) ^ rr(e, 11) ^ rr(e, 25)) +
+          ((e & hash[5]) ^ (~e & hash[6])) + k[i] +
+          (w[i] = i < 16 ? w[i] : (w[i - 16] +
+            (rr(w15, 7) ^ rr(w15, 18) ^ (w15 >>> 3)) + w[i - 7] +
+            (rr(w2, 17) ^ rr(w2, 19) ^ (w2 >>> 10))) | 0);
+        var t2 = (rr(a, 2) ^ rr(a, 13) ^ rr(a, 22)) +
+          ((a & hash[1]) ^ (a & hash[2]) ^ (hash[1] & hash[2]));
+        hash = [(t1 + t2) | 0].concat(hash);
+        hash[4] = (hash[4] + t1) | 0;
+      }
+      for (var i = 0; i < 8; i++) hash[i] = (hash[i] + old[i]) | 0;
+    }
+    for (var i = 0; i < 8; i++) {
+      for (var j = 3; j + 1; j--) {
+        var b = (hash[i] >> (j * 8)) & 255;
+        result += (b < 16 ? "0" : "") + b.toString(16);
+      }
+    }
+    return result;
+  }
+  function utf8Bytes(str) { return unescape(encodeURIComponent(str)); }
   function hashPassword(password, salt) {
-    var data = new TextEncoder().encode(salt + ":" + password);
-    return crypto.subtle.digest("SHA-256", data).then(function (buf) {
-      return Array.from(new Uint8Array(buf))
-        .map(function (b) { return b.toString(16).padStart(2, "0"); }).join("");
-    });
+    var data = salt + ":" + password;
+    // 优先 WebCrypto（安全上下文）；不可用时降级纯 JS SHA-256（http 部署）
+    if (window.crypto && crypto.subtle && crypto.subtle.digest) {
+      var encoded = new TextEncoder().encode(data);
+      return crypto.subtle.digest("SHA-256", encoded).then(function (buf) {
+        return Array.from(new Uint8Array(buf))
+          .map(function (b) { return b.toString(16).padStart(2, "0"); }).join("");
+      }).catch(function () { return sha256Js(utf8Bytes(data)); });
+    }
+    return Promise.resolve(sha256Js(utf8Bytes(data)));
   }
 
   /* 默认演示账号（Ant Design Pro 风格重构新增）：纯静态部署（无 core/auth

web/shared/session.js

@@ -124,18 +124,20 @@ var IAOP_SESSION = (function () {
         saveSession(d.user);
         return d.user;
       });
-      // 后端在线但拒绝（401 等）：是真实鉴权失败，不降级
-      return r.json().then(function (d) {
-        throw new Error((d && d.error) || "用户名或密码错误");
-      });
-    }).catch(function (e) {
-      if (e && e.message && e.message !== "timeout" &&
-          e.message !== "no backend session" &&
-          e.message !== "Failed to fetch" &&
-          e.name !== "TypeError" && !/fetch/i.test(e.message || "")) {
-        throw e; // 后端鉴权失败，直接抛
+      // 4xx = 后端在线且拒绝（真实鉴权失败）；5xx/网关错误 = 后端不可用，降级本地
+      if (r.status >= 400 && r.status < 500) {
+        return r.text().then(function (t) {
+          var msg = "用户名或密码错误";
+          try { msg = (JSON.parse(t) || {}).error || msg; } catch (e) {}
+          var err = new Error(msg);
+          err.authReject = true;
+          throw err;
+        });
       }
-      // 后端不可达 → 本地账号校验
+      throw new Error("backend-http-" + r.status);
+    }).catch(function (e) {
+      if (e && e.authReject) throw e; // 后端鉴权失败，不降级
+      // 超时 / 网络错误 / 5xx / 响应非 JSON 等一切后端不可用情形 → 本地账号校验
       if (typeof UserStore === "undefined") {
         throw new Error("认证服务不可用，且本地账号存储未加载");
       }