i18n: live-swap chat sidebar labels on language toggle

The strategic log content already refreshes via HTMX on lang-changed
(server-side translation lookup), but the chat sidebar's static labels
— title, hint, helper lede, textarea placeholder, Send button — were
baked into the HTML by Jinja at page render and only updated after a
full reload.

Add a tiny client-side i18n dictionary (CASSANDRA_I18N) plus
applyI18n(lang) in base.html. cassandraSetLang() now calls
applyI18n(newLang) right after the language PATCH succeeds and before
firing the HTMX triggers, so labels swap in step with the AI content.

Convention: <element data-i18n="key">…</element> sets textContent;
<input data-i18n-placeholder="key" …> sets .placeholder. Initial
render still goes through the existing {% if user_lang == 'it' %}
Jinja blocks so there's no flash of English on page load for IT users
— applyI18n is a no-op until the toggle is clicked.

Only the chat sidebar has bindings today. Adding more labels later is
a matter of dropping a key into the dict and tagging the element.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/templates/base.html

@@ -154,6 +154,40 @@
       try { localStorage.setItem('cassandra.theme', newTheme); } catch (e) {}
     };
 
+    // Static-label i18n dictionary. AI-generated content is re-fetched via
+    // HTMX (server-side translation), but plain UI labels are baked into
+    // the HTML at render time. This dict + applyI18n() below let the
+    // language toggle swap labels live without a page refresh.
+    // Convention: <element data-i18n="key">… (sets textContent),
+    //             <element data-i18n-placeholder="key" placeholder="…"> (sets .placeholder).
+    // First-render correctness is handled by the template's
+    // {% if user_lang == 'it' %} block — applyI18n only kicks in on
+    // subsequent toggle events.
+    window.CASSANDRA_I18N = {
+      'chat.title':       { en: 'Ask Cassandra',
+                            it: 'Chiedi a Cassandra' },
+      'chat.hint':        { en: 'grounded on the latest log + live data',
+                            it: "basato sull'ultimo log + dati in tempo reale" },
+      'chat.lede':        { en: "Ask about today's analysis. The model sees the latest strategic log, live market readings across all groups, and the last 24h of thesis-filtered headlines. Refresh wipes this conversation.",
+                            it: "Fai domande sull'analisi di oggi. Il modello vede l'ultimo log strategico, le quotazioni di mercato in tempo reale per tutti i gruppi e le ultime 24h di titoli filtrati per tesi. Un refresh della pagina cancella questa conversazione." },
+      'chat.placeholder': { en: 'e.g. why is the defence sleeve flat through Hormuz?',
+                            it: 'es. perché il comparto difesa è piatto nonostante Hormuz?' },
+      'chat.send':        { en: 'Send',
+                            it: 'Invia' },
+    };
+    window.cassandraApplyI18n = function (lang) {
+      document.querySelectorAll('[data-i18n]').forEach(function (el) {
+        var key = el.getAttribute('data-i18n');
+        var entry = window.CASSANDRA_I18N[key];
+        if (entry && entry[lang] != null) el.textContent = entry[lang];
+      });
+      document.querySelectorAll('[data-i18n-placeholder]').forEach(function (el) {
+        var key = el.getAttribute('data-i18n-placeholder');
+        var entry = window.CASSANDRA_I18N[key];
+        if (entry && entry[lang] != null) el.placeholder = entry[lang];
+      });
+    };
+
     window.cassandraSetLang = async function (newLang) {
       var pill = document.getElementById('lang-toggle');
       if (!pill) return;
@@ -170,6 +204,8 @@
           body: JSON.stringify({lang: newLang}),
         });
         if (!r.ok) throw new Error('HTTP ' + r.status);
+        // Swap any static UI labels that have i18n bindings.
+        window.cassandraApplyI18n(newLang);
         // Trigger HTMX-driven panels to re-fetch in the new language.
         // Same shape as cassandraSetTone — every panel that listens to
         // tone-changed also listens to lang-changed.

app/templates/log.html

@@ -33,28 +33,18 @@
     {% if paid %}
     <aside id="chat-sidebar" class="log-page__chat">
       <div class="chat-header">
-        <span class="chat-title">{% if user_lang == 'it' %}Chiedi a Cassandra{% else %}Ask Cassandra{% endif %}</span>
+        <span class="chat-title" data-i18n="chat.title">{% if user_lang == 'it' %}Chiedi a Cassandra{% else %}Ask Cassandra{% endif %}</span>
-        <span class="chat-hint">{% if user_lang == 'it' %}basato sull'ultimo log + dati in tempo reale{% else %}grounded on the latest log + live data{% endif %}</span>
+        <span class="chat-hint" data-i18n="chat.hint">{% if user_lang == 'it' %}basato sull'ultimo log + dati in tempo reale{% else %}grounded on the latest log + live data{% endif %}</span>
       </div>
       <div id="chat-thread" class="chat-thread">
-        <div class="chat-msg chat-msg--system">
+        <div class="chat-msg chat-msg--system" data-i18n="chat.lede">{% if user_lang == 'it' %}Fai domande sull'analisi di oggi. Il modello vede l'ultimo log strategico, le quotazioni di mercato in tempo reale per tutti i gruppi e le ultime 24h di titoli filtrati per tesi. Un refresh della pagina cancella questa conversazione.{% else %}Ask about today's analysis. The model sees the latest strategic log, live market readings across all groups, and the last 24h of thesis-filtered headlines. Refresh wipes this conversation.{% endif %}</div>
-          {% if user_lang == 'it' %}
-          Fai domande sull'analisi di oggi. Il modello vede l'ultimo log
-          strategico, le quotazioni di mercato in tempo reale per tutti i
-          gruppi e le ultime 24h di titoli filtrati per tesi. Un refresh
-          della pagina cancella questa conversazione.
-          {% else %}
-          Ask about today's analysis. The model sees the latest strategic log,
-          live market readings across all groups, and the last 24h of
-          thesis-filtered headlines. Refresh wipes this conversation.
-          {% endif %}
-        </div>
       </div>
       <form id="chat-form" class="chat-form" autocomplete="off">
         <textarea id="chat-input" rows="2"
+                  data-i18n-placeholder="chat.placeholder"
                   placeholder="{% if user_lang == 'it' %}es. perché il comparto difesa è piatto nonostante Hormuz?{% else %}e.g. why is the defence sleeve flat through Hormuz?{% endif %}"
                   required></textarea>
-        <button id="chat-send" type="submit">{% if user_lang == 'it' %}Invia{% else %}Send{% endif %}</button>
+        <button id="chat-send" type="submit" data-i18n="chat.send">{% if user_lang == 'it' %}Invia{% else %}Send{% endif %}</button>
       </form>
     </aside>
     {% else %}