feat(comments): v2 — HTMX, Turnstile, reactions, design refresh

- Extract comment templates into reusable partials (_comment.html,
  _comment_form.html, _comment_list.html, _reply_form.html, etc.)
- Add HTMX progressive enhancement: inline form submission with
  partial responses, delta polling for live updates, form reset on
  success, success/moderation toast feedback
- Integrate Cloudflare Turnstile for invisible bot protection:
  server-side token validation with hostname check, fail-closed on
  errors/timeouts, feature-flagged via TURNSTILE_SECRET_KEY env var
- Auto-approve comments that pass Turnstile; keep manual approval
  as fallback when Turnstile is disabled (model default stays False)
- Add CommentReaction model with UniqueConstraint for session-based
  anonymous reactions (heart/thumbs-up), toggle support, separate
  rate-limit bucket (20/min)
- Add comment poll endpoint (GET /comments/poll/<id>/?after_id=N)
  for HTMX delta polling without duplicates
- Update CSP middleware to allow challenges.cloudflare.com in
  script-src, connect-src, and frame-src
- Self-host htmx.min.js (v2.0.4) to minimize CSP surface area
- Add django-htmx middleware and requests to dependencies
- Add Unapprove bulk action to Wagtail admin for moderation
- Extend PII purge command to anonymize reaction session_key
- Design refresh: neon glow avatars, solid hover shadows, gradient
  section header, cyan reply borders, grid-pattern empty state,
  neon-pink focus glow on form inputs
- Add turnstile_site_key to template context via context processor
- 18 new tests covering HTMX contracts, Turnstile success/failure/
  timeout/hostname-mismatch, polling deltas, reaction toggle/dedup/
  rate-limit, CSP headers, and PII purge extension

Closes #43

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

templates/comments/confirm_bulk_unapprove.html

@@ -0,0 +1,53 @@
+{% extends 'wagtailadmin/bulk_actions/confirmation/base.html' %}
+{% load i18n wagtailusers_tags wagtailadmin_tags %}
+
+{% block titletag %}
+  {% if items|length == 1 %}
+    {% blocktrans trimmed with snippet_type_name=model_opts.verbose_name %}Unapprove {{ snippet_type_name }}{% endblocktrans %} - {{ items.0.item }}
+  {% else %}
+    {% blocktrans trimmed with count=items|length|intcomma %}Unapprove {{ count }} comments{% endblocktrans %}
+  {% endif %}
+{% endblock %}
+
+{% block header %}
+  {% trans "Unapprove" as unapprove_str %}
+  {% if items|length == 1 %}
+    {% include "wagtailadmin/shared/header.html" with title=unapprove_str subtitle=items.0.item icon=header_icon only %}
+  {% else %}
+    {% include "wagtailadmin/shared/header.html" with title=unapprove_str subtitle=model_opts.verbose_name_plural|capfirst icon=header_icon only %}
+  {% endif %}
+{% endblock header %}
+
+{% block items_with_access %}
+  {% if items %}
+    {% if items|length == 1 %}
+      <p>{% blocktrans trimmed with snippet_type_name=model_opts.verbose_name %}Unapprove this {{ snippet_type_name }}?{% endblocktrans %}</p>
+    {% else %}
+      <p>{% blocktrans trimmed with count=items|length|intcomma %}Unapprove {{ count }} selected comments?{% endblocktrans %}</p>
+      <ul>
+        {% for snippet in items %}
+          <li><a href="{{ snippet.edit_url }}" target="_blank" rel="noreferrer">{{ snippet.item }}</a></li>
+        {% endfor %}
+      </ul>
+    {% endif %}
+  {% endif %}
+{% endblock items_with_access %}
+
+{% block items_with_no_access %}
+  {% if items_with_no_access|length == 1 %}
+    {% trans "You don't have permission to unapprove this comment" as no_access_msg %}
+  {% else %}
+    {% trans "You don't have permission to unapprove these comments" as no_access_msg %}
+  {% endif %}
+  {% include 'wagtailsnippets/bulk_actions/list_items_with_no_access.html' with items=items_with_no_access no_access_msg=no_access_msg %}
+{% endblock items_with_no_access %}
+
+{% block form_section %}
+  {% if items %}
+    {% trans "Yes, unapprove" as action_button_text %}
+    {% trans "No, go back" as no_action_button_text %}
+    {% include 'wagtailadmin/bulk_actions/confirmation/form.html' %}
+  {% else %}
+    {% include 'wagtailadmin/bulk_actions/confirmation/go_back.html' %}
+  {% endif %}
+{% endblock form_section %}