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>

tests/test_printer_form.py

@@ -0,0 +1,46 @@
+"""Tests for printer form template wiring — inline driver upload + OOB select."""
+from fastapi.testclient import TestClient
+
+
+def test_printer_form_has_inline_driver_upload(client: TestClient) -> None:
+    """GET /printers renders printer form with:
+    - Driver <select> with stable id="printer-form-driver-select"
+    - Inline upload form with caller=printer_form hidden field
+    - hx-post="/drivers/upload" NOT nested inside the printer <form>
+    """
+    resp = client.get("/printers")
+    assert resp.status_code == 200
+    html = resp.text
+
+    # Driver select has stable id for OOB swap target
+    assert 'id="printer-form-driver-select"' in html, (
+        "Printer form driver <select> must have id=\"printer-form-driver-select\" "
+        "for HTMX OOB swap to work"
+    )
+
+    # Inline upload form posts caller=printer_form sentinel
+    assert 'name="caller"' in html, "Inline upload form missing name=\"caller\" field"
+    assert 'value="printer_form"' in html, (
+        "Inline upload form missing value=\"printer_form\" sentinel"
+    )
+
+    # Inline upload form targets /drivers/upload
+    assert 'hx-post="/drivers/upload"' in html, (
+        "Inline upload form missing hx-post=\"/drivers/upload\""
+    )
+
+    # CRITICAL: hx-post="/drivers/upload" must NOT be nested inside the printer form.
+    # Split on the printer form boundary and verify the upload endpoint is not inside it.
+    # The printer form always starts with hx-post="/printers" and ends at its </form>.
+    printer_form_start = html.find('hx-post="/printers"')
+    assert printer_form_start != -1, "Printer form hx-post not found — template changed?"
+
+    # Find the first </form> after the printer form opening tag
+    printer_form_end = html.find("</form>", printer_form_start)
+    assert printer_form_end != -1, "Printer form closing </form> not found"
+
+    printer_form_chunk = html[printer_form_start:printer_form_end]
+    assert 'hx-post="/drivers/upload"' not in printer_form_chunk, (
+        "hx-post=\"/drivers/upload\" must NOT be nested inside the printer <form> — "
+        "HTML forbids nested forms and browsers silently ignore the inner one"
+    )