feat(theme): 砂狼白子主题 —— 真实立绘/头像 + 自绘装饰

素材（第三方，仅个人自用）：
- 立绘/头像来自 SchaleDB（schaledb.com），学生 Id 10010 = 砂狼白子
- 版权归 NEXON Games / Yostar（蔚蓝档案），来源与公开部署提示见 README「主题」章节

自绘装饰（SVG/CSS，按公开设定还原）：
- 天蓝围巾飘带（顶栏底边）、公路车（左下角 + 加载车轮）
- 光环水印：倾斜椭圆环 + 四方位带圆头短杆（对齐官方造型，此前误画为正圆+三角）
- 倒十字发饰分组标识、迷你光环状态点

其他：主题切换（settings.theme / ?theme= / 顶栏按钮）、立绘位 settings.artwork
修复：dataFilter=uptimerobot 时平均延迟恒为「–」（改为纯外部来源时以其为唯一口径）

public/assets/app.js

@@ -1,4 +1,4 @@
-const VERSION = '0.6.0';
+const VERSION = '0.7.0';
 const HB_LIMIT = 48;
 const UPTIME_DAYS = 90;
 const BROWSER_CONCURRENCY = 6;
@@ -15,6 +15,7 @@ const state = {
   source: null,
   filter: 'all',
   view: 'cards',
+  theme: 'default',
   refreshTimer: null,
   nextRefreshAt: 0,
   loading: false,
@@ -537,6 +538,8 @@ function localStats() {
   let latCount = 0;
   let uptimeUp = 0;
   let uptimeTotal = 0;
+  // 与探针口径一致：混合来源时平均延迟只统计自建探测；若展示集合只有外部数据源，则以其延迟为唯一口径
+  const hasProbe = monitors.some((m) => !isExternal(m));
   for (const m of monitors) {
     const st = state.status?.monitors?.[m.id];
     if (!st || st.status === 'pending') {
@@ -545,8 +548,7 @@ function localStats() {
     }
     if (st.status === 'up') up++;
     else down++;
-    // 与探针口径一致：平均延迟只统计自建探测目标
-    if (!isExternal(m) && st.latency != null) {
+    if (st.latency != null && (!isExternal(m) || !hasProbe)) {
       latSum += st.latency;
       latCount++;
     }
@@ -666,7 +668,10 @@ function setLoading(on, text = '刷新中…') {
   state.loading = on;
   const btn = $('refresh-btn');
   btn.disabled = on;
-  btn.textContent = on ? text : '刷新';
+  // 车轮图标（砂狼白子骑行意象，主题里会转起来）
+  btn.innerHTML = on
+    ? `<svg class="wheel" viewBox="0 0 24 24" aria-hidden="true"><circle cx="12" cy="12" r="10" fill="none" stroke="currentColor" stroke-width="2" opacity="0.35"/><g stroke="currentColor" stroke-width="1.3"><line x1="12" y1="2" x2="12" y2="22"/><line x1="2" y1="12" x2="22" y2="12"/><line x1="4.9" y1="4.9" x2="19.1" y2="19.1"/><line x1="19.1" y1="4.9" x2="4.9" y2="19.1"/></g><circle cx="12" cy="12" r="2.2" fill="currentColor"/></svg><span>${escapeHtml(text)}</span>`
+    : '刷新';
 }
 
 async function refresh({ force = false } = {}) {
@@ -748,9 +753,55 @@ function startAutoRefresh() {
   }, 1000);
 }
 
+/* ---------- 主题 ---------- */
+
+const THEMES = { default: '默认', shiroko: '砂狼白子' };
+
+function resolveTheme() {
+  const q = new URLSearchParams(location.search).get('theme');
+  let saved = null;
+  try {
+    saved = localStorage.getItem('shiroko.theme');
+  } catch { /* 隐私模式 */ }
+  return [q, saved, state.config?.settings?.theme].find((t) => t && THEMES[t]) ?? 'default';
+}
+
+// 角色立绘位：主题为白子且配置了 artwork 时才插入；文件不存在则静默移除（不留破图）
+function applyArtwork() {
+  document.querySelector('.artwork')?.remove();
+  const src = state.config?.settings?.artwork;
+  if (state.theme !== 'shiroko' || !src) return;
+  const img = document.createElement('img');
+  img.className = 'artwork';
+  img.alt = '';
+  img.src = src;
+  img.addEventListener('error', () => img.remove());
+  document.body.appendChild(img);
+}
+
+function applyTheme(theme, { persist = true } = {}) {
+  state.theme = THEMES[theme] ? theme : 'default';
+  if (state.theme === 'default') delete document.body.dataset.theme;
+  else document.body.dataset.theme = state.theme;
+  if (persist) {
+    try {
+      localStorage.setItem('shiroko.theme', state.theme);
+    } catch { /* 忽略 */ }
+  }
+  const icon = document.querySelector('link[rel="icon"]');
+  if (icon) icon.setAttribute('href', state.theme === 'shiroko' ? 'assets/favicon-shiroko.png' : 'assets/favicon.svg');
+  applyArtwork();
+  const btn = $('theme-btn');
+  if (btn) {
+    btn.classList.toggle('active', state.theme === 'shiroko');
+    btn.title = state.theme === 'shiroko' ? '当前主题：砂狼白子（点击切回默认）' : '当前主题：默认（点击切换到砂狼白子主题）';
+  }
+}
+
 function bindEvents() {
   // 只有手动点「刷新」才会触发一次重新检测；自动刷新是只读的
   $('refresh-btn').addEventListener('click', () => refresh({ force: true }));
+  $('theme-btn')?.addEventListener('click', () => applyTheme(state.theme === 'shiroko' ? 'default' : 'shiroko'));
 }
 
 /* ---------- 启动 ---------- */
@@ -767,6 +818,7 @@ async function init() {
   $('site-desc').textContent = state.config.settings?.description || '';
   const versionEl = document.querySelector('.version');
   if (versionEl) versionEl.textContent = `shiroko-monitor v${VERSION}`;
+  applyTheme(resolveTheme());
   await resolveSource();
   state.view = resolveView();
   bindEvents();