Add MrTerm Web: self-hosted browser version (Docker Compose) with user accounts, per-user vaults encrypted by the login password, the desktop UI over WebSocket, SFTP upload/download over HTTP; share backend channels between Android and web (src/core/backend.js)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/web/public/login.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8" />
+  <meta name="viewport" content="width=device-width, initial-scale=1" />
+  <title>MrTerm</title>
+  <link rel="icon" href="/favicon.png" />
+  <link rel="stylesheet" href="/app/src/renderer/app-themes.css" />
+  <link rel="stylesheet" href="/web/login.css" />
+</head>
+<body>
+  <main class="box">
+    <img src="/favicon.png" alt="" class="logo" />
+    <h1>Mr<span>Term</span></h1>
+    <p id="intro"></p>
+    <form id="form" autocomplete="on">
+      <label><span data-t="Username">Username</span><input name="name" autocomplete="username" required autofocus /></label>
+      <label><span data-t="Password">Password</span><input name="password" type="password" autocomplete="current-password" required /></label>
+      <label id="repeatRow" hidden><span data-t="Repeat password">Repeat password</span><input name="repeat" type="password" autocomplete="new-password" /></label>
+      <div id="err" class="err" hidden></div>
+      <button id="submit" type="submit"></button>
+    </form>
+    <div class="ver" id="ver"></div>
+  </main>
+  <script src="/app/src/i18n.js"></script>
+  <script src="/web/login.js"></script>
+</body>
+</html>