feat: memory-only sessions on HTTP, streamed exports, UI refresh

Session

- COOKIE_SECURE=false no longer persists the owner key for ten years.
  services/session.cookie_kwargs() drops max_age in that mode, so the
  browser holds the key in memory and the session ends with the window.
  Everything still persists server-side; only the browser link is
  temporary. base.html shows a warning banner (FR/EN) and an extra
  paragraph in the onboarding modal, and the README explains the
  trade-off and the backup-key escape hatch.
- Both cookie writers (middleware, POST /session/restore) go through
  cookie_kwargs() so the policy cannot drift between them.
- The CSRF guard on /session/restore compared request.url.scheme against
  the Origin header. Behind a TLS-terminating proxy uvicorn sees http
  while the browser sends https, so every legitimate restore was
  rejected with 403. It now compares hosts only, including
  X-Forwarded-Host.
- /static/*, /favicon.ico and /robots.txt skip the middleware. Each
  cookieless hit was inserting an Owner row no browser could ever use.

Reliability

- Malformed printer-form FK fields no longer escape as HTTP 500:
  a non-numeric client_id/driver_id raised ValueError and an unknown
  driver_id hit a FOREIGN KEY constraint. Both are now 400/404 HTMX
  fragments, and the duplicated field checks moved into
  _validate_fields().
- Package exports stream. build_intunewin() encrypts the inner ZIP in
  1 MB chunks against temp files with a streaming HMAC and SHA256, and
  both endpoints serve the result with FileResponse plus a background
  cleanup task. A 100 MB driver used to be held in memory three or four
  times over per concurrent download. The byte layout is unchanged.
- FileResponse also escapes the download filename, which was previously
  interpolated raw into Content-Disposition.
- python-multipart >= 0.0.18 (CVE-2024-53981, reachable from
  /drivers/upload) and Pillow >= 10.3 (CVE-2024-28219, reachable from
  icon upload).
- icons.py reads cfg.ICONS_DIR instead of re-deriving the path from
  DATA_DIR, matching the .intunewin export.

UI

- Sidebar/topbar shell, inline SVG icon macros (partials/icons.html),
  card and data-table components, grouped printer list, and the
  dedicated /printers/new page replacing partials/printer_form.html.

Tests

- 194 pass with a bare `pytest tests/`: tests/conftest.py now forces
  cfg.COOKIE_SECURE = False like the e2e conftest already did, so the
  Secure cookie is no longer dropped over http://testserver.
- New coverage for the malformed-FK guards, the chunk-boundary cases in
  the encrypt loop (every residue mod _CHUNK plus a multi-megabyte
  payload), temp-dir cleanup after both exports, and the whole
  COOKIE_SECURE matrix.
- test_printer_edit.py located the Edit button by its translated label,
  so it only passed on English-locale machines. It now targets the
  showModal() hook, which also cuts the e2e run from 84s to 15s.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

imptune/templates/session_restore.html

@@ -1,20 +1,35 @@
 {% extends "base.html" %}
+{% import "partials/icons.html" as ico %}
+
+{% block head_title %}Restore backup key · ImpTune{% endblock %}
+{% block page_title %}<span x-data x-text="$store.i18n.t('restore_title')">Restore a backup key</span>{% endblock %}
 
 {% block content %}
-<h1>Restore backup key</h1>
+<section class="card" style="max-width:34rem">
+  <div class="card-head">
+    {{ ico.i('key') }}
+    <h2 x-data x-text="$store.i18n.t('restore_title')">Restore a backup key</h2>
+  </div>
+  <div class="card-body">
+    <p class="dim" x-data x-text="$store.i18n.t('restore_desc')">
+      Paste the key from <code>imptune-backup-key.txt</code> to get your printers,
+      settings, and clients back in this browser.
+    </p>
 
-<p>Paste the key from your <code>imptune-backup-key.txt</code> backup file to
-recover your printers, configs, and groups on this browser.</p>
+    {% if error %}
+    <div class="error"><p>{{ error }}</p></div>
+    {% endif %}
 
-{% if error %}
-<div class="error"><p>{{ error }}</p></div>
-{% endif %}
-
-<form method="post" action="/session/restore">
-  <label>
-    Backup key
-    <input type="text" name="key" placeholder="paste your key here" required autofocus>
-  </label>
-  <button type="submit">Restore</button>
-</form>
+    <form method="post" action="/session/restore">
+      <label>
+        <span class="label-text" x-data x-text="$store.i18n.t('backup_key_label')">Backup key</span>
+        <input type="text" name="key" class="mono" placeholder="paste your key here" required autofocus>
+      </label>
+      <div class="btn-row" style="margin-top:.9rem">
+        <button type="submit" class="btn" x-data x-text="$store.i18n.t('restore_btn')">Restore</button>
+        <a href="/" class="btn ghost" x-data x-text="$store.i18n.t('cancel')">Cancel</a>
+      </div>
+    </form>
+  </div>
+</section>
 {% endblock %}