feat(03-02): implement printer detail page with driver info and regenerate placeholder

- Add GET /printers/{printer_id} route to pages.py with LEFT OUTER JOINs on Client and Driver
- Create printer_detail.html full-page template showing all config fields and driver info
- Display "No driver assigned" when driver FK is null
- Add disabled "Regenerate Package" button (Phase 4 placeholder)
- Make printer names in printer_list.html clickable links to detail page

imptune/templates/partials/printer_list.html

@@ -22,7 +22,7 @@
       <tbody>
         {% for p in printers %}
         <tr>
-          <td>{{ p.name }}</td>
+          <td><a href="/printers/{{ p.id }}">{{ p.name }}</a></td>
           <td>{{ p.ip_address }}</td>
           <td>{{ p.port_name }}</td>
           <td>{{ p.driver.original_filename if p.driver_id else '—' }}</td>