Remove the Go reference server; keep only Rust

The Go implementation is preserved in the v1.0.0 tag. Its observable
behaviour stays the API reference: responses recorded from the Go server
live in tools/compatibility_expected.txt, and tools/compatibility.py now
compares the Rust server against them (--update re-records after an
intentional change). The Go SQLite schema is frozen in
tests/fixtures/go_schema_v1.sql for the existing-database test.

Move the web client from internal/httpapi/web to web/, drop the Go CI job
and Go version pin, and update README, AGENTS.md and docs.

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

web/index.html

@@ -0,0 +1,106 @@
+<!doctype html>
+<html lang="ru">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
+  <meta name="theme-color" content="#5b5bd6">
+  <meta name="description" content="Balance — личные финансы на вашем сервере">
+  <title>Balance</title>
+  <link rel="icon" href="/icon.svg" type="image/svg+xml">
+  <link rel="manifest" href="/manifest.webmanifest">
+  <link rel="stylesheet" href="/styles.css">
+</head>
+<body>
+  <div id="toast-region" class="toast-region" aria-live="polite" aria-atomic="true"></div>
+
+  <main id="auth-view" class="auth-layout">
+    <section class="auth-card" aria-labelledby="auth-title">
+      <div class="brand brand-auth">
+        <img src="/icon.svg" alt="" width="58" height="58">
+        <div>
+          <span class="brand-name">Balance</span>
+          <span class="brand-caption">Ваши финансы. Ваш сервер.</span>
+        </div>
+      </div>
+      <div class="auth-copy">
+        <p class="eyebrow">SELF-HOSTED</p>
+        <h1 id="auth-title">Финансы под вашим контролем</h1>
+        <p>Войдите в аккаунт этого сервера. Операции синхронизируются с iPhone, Apple Watch, Mac и Android.</p>
+      </div>
+      <div class="segmented auth-switch" role="tablist" aria-label="Вход или регистрация">
+        <button type="button" class="is-active" data-auth-mode="login" role="tab">Войти</button>
+        <button type="button" data-auth-mode="register" role="tab">Регистрация</button>
+      </div>
+      <form id="auth-form" class="stack" autocomplete="on">
+        <label class="field">
+          <span>Email</span>
+          <input id="auth-email" name="email" type="email" inputmode="email" autocomplete="email" required maxlength="254" placeholder="name@example.com">
+        </label>
+        <label class="field">
+          <span>Пароль</span>
+          <input id="auth-password" name="password" type="password" autocomplete="current-password" required minlength="8" maxlength="1024" placeholder="Минимум 8 символов">
+        </label>
+        <p id="auth-error" class="form-error" role="alert" hidden></p>
+        <button id="auth-submit" class="button button-primary button-large" type="submit">Войти</button>
+      </form>
+      <p class="security-note"><span aria-hidden="true">🔒</span> Сессия хранится в защищённых HttpOnly-cookie и недоступна JavaScript.</p>
+    </section>
+  </main>
+
+  <div id="app-view" class="app-shell" hidden>
+    <aside class="sidebar">
+      <div class="brand sidebar-brand">
+        <img src="/icon.svg" alt="" width="42" height="42">
+        <div>
+          <span class="brand-name">Balance</span>
+          <span class="brand-caption">Личные финансы</span>
+        </div>
+      </div>
+      <nav class="side-nav" aria-label="Основная навигация">
+        <button type="button" data-route="dashboard"><span>⌂</span> Обзор</button>
+        <button type="button" data-route="transactions"><span>↕</span> Операции</button>
+        <button type="button" data-route="analytics"><span>◫</span> Аналитика</button>
+        <button type="button" data-route="budgets"><span>◎</span> Бюджеты</button>
+        <button type="button" data-route="categories"><span>◆</span> Категории</button>
+        <button type="button" data-route="settings"><span>⚙</span> Настройки</button>
+      </nav>
+      <div class="sidebar-footer">
+        <div id="sync-pill" class="sync-pill"><span></span><span>Синхронизировано</span></div>
+        <div class="account-mini">
+          <div class="avatar" id="account-avatar">Б</div>
+          <div>
+            <strong id="account-email">—</strong>
+            <span>Личный аккаунт</span>
+          </div>
+        </div>
+      </div>
+    </aside>
+
+    <main class="workspace">
+      <header class="mobile-header">
+        <div class="brand">
+          <img src="/icon.svg" alt="" width="36" height="36">
+          <span class="brand-name">Balance</span>
+        </div>
+        <button type="button" class="icon-button" data-action="sync" aria-label="Синхронизировать">↻</button>
+      </header>
+      <div id="content" class="content" tabindex="-1"></div>
+    </main>
+
+    <nav class="bottom-nav" aria-label="Мобильная навигация">
+      <button type="button" data-route="dashboard"><span>⌂</span><small>Обзор</small></button>
+      <button type="button" data-route="transactions"><span>↕</span><small>Операции</small></button>
+      <button type="button" data-route="analytics"><span>◫</span><small>Аналитика</small></button>
+      <button type="button" data-route="budgets"><span>◎</span><small>Бюджеты</small></button>
+      <button type="button" data-route="settings"><span>⚙</span><small>Ещё</small></button>
+    </nav>
+  </div>
+
+  <dialog id="editor-dialog" class="modal">
+    <div id="dialog-content"></div>
+  </dialog>
+
+  <noscript>Для работы Balance необходимо включить JavaScript.</noscript>
+  <script src="/app.js" defer></script>
+</body>
+</html>