feat(11-01): UIE-02 — dedicated Add Printer page at GET /printers/new

- Create imptune/templates/printers_new.html: full page extending base.html
  with plain <form action="/printers" method="post"> (no HTMX, browser follows 303)
  and inline driver upload sub-form
- Update imptune/templates/printers.html: remove inline Add Printer form,
  add <a href="/printers/new" role="button">Add Printer</a> link
- Add GET /printers/new route in imptune/api/pages.py (placed before /{printer_id})
- Change POST /printers to always return RedirectResponse(url='/printers', status_code=303)
- Update existing POST /printers tests to assert 303 + follow_redirects=False
- Update test_printer_form.py to check /printers/new instead of /printers (UIE-02 arch)
- UIE-02 tests GREEN; UIE-01/03 scaffolds remain RED (expected — not yet implemented)

imptune/api/printers.py

@@ -5,7 +5,7 @@ from collections import defaultdict
 from pathlib import Path
 
 from fastapi import APIRouter, Form, Request
-from fastapi.responses import HTMLResponse
+from fastapi.responses import HTMLResponse, RedirectResponse
 from fastapi.templating import Jinja2Templates
 from peewee import JOIN
 
@@ -101,7 +101,7 @@ def create_printer(
         driver=driver_fk,
     )
 
-    return _render_printer_list(request)
+    return RedirectResponse(url="/printers", status_code=303)
 
 
 @router.delete("/{printer_id}", response_class=HTMLResponse)