feat(nav): unified navbar, account page, corpus summary widget, and i18n fixes

- New includes/nav.php: sticky site-wide nav with Tools dropdown, Dashboard
  link, compact language switcher, user identity → /account.php, Log out
- New account.php: credits & plan, profile, team, usage sections
- New api/corpus-summary.php: JSON endpoint for corpus doc count + last updated
- Replaces topbar in layout.php, layout_dashboard.php, and dashboard.php
- Fixes hardcoded Norwegian strings in dashboard.php credit cards via dbnToolsT()
- Adds 35 new i18n keys across all 4 languages (en/no/uk/pl) in i18n.php
- CSS: .dbn-nav navbar + .account-* account page styles in tools.css

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

includes/nav.php

@@ -0,0 +1,102 @@
+<?php
+declare(strict_types=1);
+/**
+ * Unified site navbar — included by layout.php, layout_dashboard.php, and standalone pages.
+ * Assumes bootstrap.php (and i18n.php) has already been required.
+ */
+
+$_navGuest   = !dbnToolsIsAuthenticated();
+$_navAuth    = $_navGuest ? null : dbnToolsAuthenticatedUser();
+$_navEmail   = (string)($_navAuth['email'] ?? '');
+$_navUser    = $_navEmail !== '' ? (strstr($_navEmail, '@', true) ?: $_navEmail) : '';
+$_navLang    = dbnToolsCurrentLanguage();
+$_navTools   = dbnToolsLaunchedTools($_navLang);
+$_navPath    = strtok((string)($_SERVER['REQUEST_URI'] ?? '/'), '?') ?: '/';
+$_navOnDash  = str_starts_with($_navPath, '/dashboard');
+$_navReturnUrl = urlencode($_navPath);
+?>
+<nav class="dbn-nav" role="navigation" aria-label="<?= htmlspecialchars(dbnToolsT('suite_title', $_navLang)) ?>">
+    <a class="dbn-nav__brand" href="/dashboard.php">
+        <span class="dbn-nav__brandmark" aria-hidden="true">⚖</span>
+        <span class="dbn-nav__brandname">Do Better Norge</span>
+    </a>
+
+    <div class="dbn-nav__links" role="menubar">
+        <div class="dbn-nav__dropdown" data-nav-dropdown>
+            <button class="dbn-nav__link dbn-nav__dropper"
+                    type="button"
+                    aria-haspopup="menu"
+                    aria-expanded="false"
+                    aria-controls="navToolsPanel">
+                <?= htmlspecialchars(dbnToolsT('nav_tools', $_navLang)) ?>
+                <span class="dbn-nav__caret" aria-hidden="true">▾</span>
+            </button>
+            <div class="dbn-nav__panel" id="navToolsPanel" role="menu" aria-label="<?= htmlspecialchars(dbnToolsT('nav_tools', $_navLang)) ?>">
+<?php foreach ($_navTools as $slug => $item): ?>
+                <a class="dbn-nav__panel-item" href="<?= htmlspecialchars($item['url']) ?>" role="menuitem">
+                    <span class="dbn-nav__panel-badge" aria-hidden="true"><?= htmlspecialchars($item['icon']) ?></span>
+                    <span class="dbn-nav__panel-label"><?= htmlspecialchars($item['label']) ?></span>
+                    <span class="dbn-nav__panel-sub"><?= htmlspecialchars($item['sub']) ?></span>
+                </a>
+<?php endforeach; ?>
+            </div>
+        </div>
+
+        <a class="dbn-nav__link<?= $_navOnDash ? ' is-active' : '' ?>"
+           href="/dashboard.php"
+           role="menuitem"
+           <?= $_navOnDash ? 'aria-current="page"' : '' ?>>
+            <?= htmlspecialchars(dbnToolsT('nav_dashboard', $_navLang)) ?>
+        </a>
+    </div>
+
+    <div class="dbn-nav__right">
+        <nav class="dbn-nav__langs" aria-label="Language">
+<?php foreach (dbnToolsSupportedLanguages() as $lc): ?>
+            <a href="<?= htmlspecialchars($_navPath . '?lang=' . $lc) ?>"
+               class="dbn-nav__lang<?= $lc === $_navLang ? ' is-active' : '' ?>"
+               hreflang="<?= htmlspecialchars($lc) ?>"
+               aria-label="<?= htmlspecialchars(dbnToolsLanguageName($lc)) ?>"
+               title="<?= htmlspecialchars(dbnToolsLanguageName($lc)) ?>"><?= htmlspecialchars(strtoupper($lc)) ?></a>
+<?php endforeach; ?>
+        </nav>
+
+<?php if ($_navGuest): ?>
+        <a href="/?return=<?= $_navReturnUrl ?>" class="dbn-nav__login">
+            <?= htmlspecialchars(dbnToolsT('nav_login', $_navLang)) ?>
+        </a>
+<?php else: ?>
+        <a class="dbn-nav__account-link" href="/account.php" title="<?= htmlspecialchars($_navEmail) ?>">
+<?php if ($_navUser !== ''): ?>
+            <span class="dbn-nav__username"><?= htmlspecialchars($_navUser) ?></span>
+<?php endif; ?>
+            <span class="dbn-nav__account-badge"><?= htmlspecialchars(dbnToolsT('nav_account', $_navLang)) ?></span>
+        </a>
+        <a href="/api/logout.php" class="dbn-nav__logout">
+            <?= htmlspecialchars(dbnToolsT('nav_logout', $_navLang)) ?>
+        </a>
+<?php endif; ?>
+    </div>
+</nav>
+<script>
+(function () {
+    var dropdowns = document.querySelectorAll('[data-nav-dropdown]');
+    dropdowns.forEach(function (dd) {
+        var btn = dd.querySelector('.dbn-nav__dropper');
+        var panel = dd.querySelector('.dbn-nav__panel');
+        if (!btn || !panel) return;
+
+        function open() { dd.classList.add('is-open'); btn.setAttribute('aria-expanded', 'true'); }
+        function close() { dd.classList.remove('is-open'); btn.setAttribute('aria-expanded', 'false'); }
+        function toggle() { dd.classList.contains('is-open') ? close() : open(); }
+
+        btn.addEventListener('click', function (e) { e.stopPropagation(); toggle(); });
+        document.addEventListener('click', function (e) {
+            if (!dd.contains(e.target)) close();
+        });
+        document.addEventListener('keydown', function (e) {
+            if (e.key === 'Escape') close();
+        });
+    });
+}());
+</script>