feat: configurable VPS URL, 163 mail support, mail provider selector

- VPS URL: now an input field in Side Panel, no longer hardcoded
  - Dynamic script injection via chrome.scripting.executeScript
  - host_permissions changed to <all_urls> for flexibility
- 163 Mail: new content script (mail-163.js) with actual selectors
  - Mail items: div[sign="letter"], sender: .nui-user, subject: span.da0
  - Supports aria-label fallback for matching
- Mail provider selector: dropdown to switch between QQ Mail and 163 Mail
  - Background routes steps 4/7 to correct mail content script
- Settings persist in chrome.storage.session

sidepanel/sidepanel.css

@@ -260,6 +260,23 @@ header {
 .data-input::placeholder { color: var(--text-muted); }
 .data-input:focus { border-color: var(--blue); box-shadow: 0 0 0 3px var(--blue-soft); }
 
+.data-select {
+  flex: 1;
+  padding: 5px 8px;
+  background: var(--bg-base);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  color: var(--text-primary);
+  font-family: inherit;
+  font-size: 11px;
+  outline: none;
+  cursor: pointer;
+  transition: border-color var(--transition);
+  min-width: 0;
+}
+.data-select:focus { border-color: var(--blue); box-shadow: 0 0 0 3px var(--blue-soft); }
+[data-theme="dark"] .data-select { color-scheme: dark; }
+
 /* Status Bar */
 .status-bar {
   display: flex;

sidepanel/sidepanel.html

@@ -41,13 +41,24 @@
   <section id="data-section">
     <div class="data-card">
       <div class="data-row">
-        <span class="data-label">OAuth</span>
-        <span id="display-oauth-url" class="data-value mono truncate">Waiting...</span>
+        <span class="data-label">VPS</span>
+        <input type="text" id="input-vps-url" class="data-input" placeholder="http://ip:port/management.html#/oauth" />
+      </div>
+      <div class="data-row">
+        <span class="data-label">Mail</span>
+        <select id="select-mail-provider" class="data-select">
+          <option value="qq">QQ Mail (wx.mail.qq.com)</option>
+          <option value="163">163 Mail (mail.163.com)</option>
+        </select>
       </div>
       <div class="data-row">
         <span class="data-label">Email</span>
         <input type="text" id="input-email" class="data-input" placeholder="Paste DuckDuckGo email" />
       </div>
+      <div class="data-row">
+        <span class="data-label">OAuth</span>
+        <span id="display-oauth-url" class="data-value mono truncate">Waiting...</span>
+      </div>
       <div class="data-row">
         <span class="data-label">Callback</span>
         <span id="display-localhost-url" class="data-value mono truncate">Waiting...</span>

sidepanel/sidepanel.js

@@ -19,6 +19,8 @@ const btnAutoRun = document.getElementById('btn-auto-run');
 const btnAutoContinue = document.getElementById('btn-auto-continue');
 const autoContinueBar = document.getElementById('auto-continue-bar');
 const btnClearLog = document.getElementById('btn-clear-log');
+const inputVpsUrl = document.getElementById('input-vps-url');
+const selectMailProvider = document.getElementById('select-mail-provider');
 
 // ============================================================
 // State Restore on load
@@ -39,6 +41,12 @@ async function restoreState() {
     if (state.email) {
       inputEmail.value = state.email;
     }
+    if (state.vpsUrl) {
+      inputVpsUrl.value = state.vpsUrl;
+    }
+    if (state.mailProvider) {
+      selectMailProvider.value = state.mailProvider;
+    }
 
     if (state.stepStatuses) {
       for (const [step, status] of Object.entries(state.stepStatuses)) {
@@ -238,7 +246,7 @@ btnClearLog.addEventListener('click', () => {
   logArea.innerHTML = '';
 });
 
-// Save email on change
+// Save settings on change
 inputEmail.addEventListener('change', async () => {
   const email = inputEmail.value.trim();
   if (email) {
@@ -246,6 +254,20 @@ inputEmail.addEventListener('change', async () => {
   }
 });
 
+inputVpsUrl.addEventListener('change', async () => {
+  const vpsUrl = inputVpsUrl.value.trim();
+  if (vpsUrl) {
+    await chrome.runtime.sendMessage({ type: 'SAVE_SETTING', source: 'sidepanel', payload: { vpsUrl } });
+  }
+});
+
+selectMailProvider.addEventListener('change', async () => {
+  await chrome.runtime.sendMessage({
+    type: 'SAVE_SETTING', source: 'sidepanel',
+    payload: { mailProvider: selectMailProvider.value },
+  });
+});
+
 // ============================================================
 // Listen for Background broadcasts
 // ============================================================