feat: public sharing links for households

Add hard-to-guess public URLs (/public/<token>) that show a read-only
meal status dashboard for each household. Only people with the link can
see the data — no login required.

- models.py: public_token + public_enabled columns on households,
  get_household_by_public_token(), generate_public_token(),
  set_public_enabled()
- meals.py: /public/<token> route, /admin/public-link for
  generate/disable/enable/regenerate
- templates/public.html: clean read-only public dashboard
- templates/public-not-found.html: 404 for invalid/disabled links
- templates/dashboard.html: admin UI with copy/regenerate/disable
- static/style.css: public page and URL box styles
- i18n.py: 18 new translation keys (en/fr/de)

templates/dashboard.html

@@ -114,6 +114,27 @@
             </form>
 
             {% if is_admin %}
+            <form method="POST" action="{{ url_for('meals.admin_public_link') }}" class="manage-form">
+                <h4>🔗 {{ t('Public Sharing Link') }}</h4>
+                <p class="hint">{{ t('Share a read-only view of your household\'s meal status. The link is hard to guess — only people with it can see the data.') }}</p>
+                {% if household.public_token and household.public_enabled %}
+                <div class="public-url-box">
+                    <code>{{ request.host_url }}public/{{ household.public_token }}</code>
+                    <button type="button" class="btn btn-sm" onclick="copyPublicUrl(this)">{{ t('Copy') }}</button>
+                </div>
+                <div class="btn-row" style="margin-top: 8px;">
+                    <button type="submit" name="action" value="generate" class="btn btn-sm">{{ t('Regenerate') }}</button>
+                    <button type="submit" name="action" value="disable" class="btn btn-sm btn-danger">{{ t('Disable') }}</button>
+                </div>
+                {% elif household.public_token and not household.public_enabled %}
+                <p class="hint">{{ t('Public link is currently disabled.') }}</p>
+                <button type="submit" name="action" value="enable" class="btn btn-sm">{{ t('Enable') }}</button>
+                {% else %}
+                <p class="hint">{{ t('No public link yet. Generate one to share.') }}</p>
+                <button type="submit" name="action" value="generate" class="btn btn-sm">{{ t('Generate Link') }}</button>
+                {% endif %}
+            </form>
+
             <form method="POST" action="{{ url_for('meals.admin_set_timezone') }}" class="manage-form">
                 <h4>🕐 {{ t('Household Timezone') }}</h4>
                 <p class="hint">{{ t('Used to send reminders at 10:00 (lunch) and 16:00 (dinner) local time.') }}</p>
@@ -146,4 +167,22 @@
     </details>
 </div>
 
+<script>
+function copyPublicUrl(btn) {
+    var code = btn.parentElement.querySelector('code');
+    if (!code) return;
+    navigator.clipboard.writeText(code.textContent).then(function() {
+        var orig = btn.textContent;
+        btn.textContent = 'Copied!';
+        btn.disabled = true;
+        setTimeout(function() { btn.textContent = orig; btn.disabled = false; }, 2000);
+    }).catch(function() {
+        var range = document.createRange();
+        range.selectNode(code);
+        window.getSelection().removeAllRanges();
+        window.getSelection().addRange(range);
+    });
+}
+</script>
+
 {% endblock %}