feat(12-02): wire all template strings to Alpine i18n store

- dashboard.html: headings, quick actions, empty states wired to x-text
- printers.html: h1, add button, h2 wired to x-text
- printers_new.html: all form labels (span pattern), options, submit buttons wired
- clients.html: headings, label, submit button wired
- client_detail.html: back link, section heading wired
- drivers.html: all headings, label, buttons, spinner wired
- packages.html: heading, description, table headers, empty state wired
- printer_detail.html: all dt/dd, section headings, copy buttons, script/export links wired with conditional Jinja2 for color/collate/client
- partials/printer_list.html: table headers, Yes/No cells (Alpine ternary), delete button wired
- partials/printer_edit_modal.html: edit trigger, modal title, all labels (span pattern), options, save/cancel wired
- partials/client_list.html: empty state, table headers wired
- partials/driver_list.html: table headers, unknown values, empty state wired
- Fix test_printers_library_no_form: check form element attribute instead of UI label string (now in i18n dict)

imptune/templates/client_detail.html

@@ -2,10 +2,10 @@
 
 {% block content %}
 <h1>{{ client.name }}</h1>
-<p><a href="/clients">&larr; All Clients</a></p>
+<p><a href="/clients" x-data x-text="$store.i18n.t('back_to_clients')">&larr; All Clients</a></p>
 
 <section>
-  <h2>Printers</h2>
+  <h2 x-data x-text="$store.i18n.t('printers_section')">Printers</h2>
   {% include "partials/printer_list.html" %}
 </section>
 {% endblock %}