feat(09-01): add inline driver upload to printer form with OOB refresh

- Add id="printer-form-driver-select" to driver <select> (OOB swap target)
- Add sibling <form hx-post="/drivers/upload"> AFTER printer </form>,
  inside Alpine x-data div — avoids invalid nested form HTML
- Hidden <input name="caller" value="printer_form"> sentinel triggers OOB path
- Add hidden <div id="driver-list"> anchor for HTMX outerHTML swap target
- Create tests/test_printer_form.py with test_printer_form_has_inline_driver_upload
  asserting stable select id, caller sentinel, and non-nested upload form

Full non-e2e suite: 112 passed.

imptune/templates/partials/printer_form.html

@@ -27,7 +27,7 @@
 
     <label>
       Driver
-      <select name="driver_id">
+      <select name="driver_id" id="printer-form-driver-select">
         <option value="">-- No driver --</option>
         {% for item in driver_data %}
         <option value="{{ item.driver.id }}"
@@ -83,4 +83,17 @@
 
     <button type="submit">Save Printer</button>
   </form>
+
+  <form hx-post="/drivers/upload"
+        hx-target="#driver-list"
+        hx-encoding="multipart/form-data"
+        hx-swap="outerHTML">
+    <input type="hidden" name="caller" value="printer_form">
+    <label>
+      Upload New Driver
+      <input type="file" name="file" accept=".zip" required>
+    </label>
+    <button type="submit" class="secondary">Upload Driver</button>
+  </form>
+  <div id="driver-list" style="display:none"></div>
 </div>