Style every MFA screen through the element system

The MFA pages (manage, TOTP activate/deactivate, recovery codes, security keys,
reauthenticate) are built almost entirely from allauth's `element` primitives, so
they are styled by overriding the elements rather than by rewriting eight page
templates. New allauth pages then inherit the look for free.

- field + img elements were missing entirely, so allauth fell back to bare HTML:
  the TOTP secret and recovery-code list rendered as unstyled inputs. The QR now
  sits on a white plate -- it is dark modules on a transparent ground, so on the
  dark theme it was dark-on-dark and phones could not scan it.
- button now honours the tags allauth sets. They were all flattened to
  btn-primary, which made "Deactivate" look exactly as safe as "View".
- the `code` field renders as a daisyUI otp wherever it appears, so the
  reauthenticate and activate pages get the same input as the login challenge.
  The boxes step aside past six characters: allauth accepts a TOTP code (6) or a
  recovery code (8) in that one field.

Fixes a crash: the security-key list does {% load humanize %}, which raised
TemplateSyntaxError because django.contrib.humanize was not installed. That page
500'd on every request; it is now installed and covered by a test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

templates/allauth/elements/fields.html

@@ -41,7 +41,25 @@
                 </label>
             {% endif %}
             {% with icon=field|field_icon %}
-                {% if icon %}
+                {% if field|is_otp %}
+                    {% comment %}
+                        daisyUI's otp is one input overlaid on the boxes, and it sizes itself from
+                        its `span` children — so the sr-only label goes OUTSIDE the container, or it
+                        would count as a seventh box and throw the width off.
+                    {% endcomment %}
+                    {% if attrs.unlabeled %}<label class="sr-only" for="{{ field.id_for_label }}">{{ field.label }}</label>{% endif %}
+                    <div class="flex justify-center">
+                        <div class="otp otp-lg" data-otp>
+                            {{ field|daisy:"" }}
+                            <span></span>
+                            <span></span>
+                            <span></span>
+                            <span></span>
+                            <span></span>
+                            <span></span>
+                        </div>
+                    </div>
+                {% elif icon %}
                     <label class="input flex w-full items-center gap-2 {% if field.errors %}input-error{% endif %}" for="{{ field.id_for_label }}">
                         <span class="opacity-50">{% lucide icon size=16 %}</span>
                         {% if attrs.unlabeled %}<span class="sr-only">{{ field.label }}</span>{% endif %}