fix(library): use {% comment %} for multi-line template comments

Django's `{# #}` syntax only supports single-line comments; multi-line
blocks were rendering as literal text in the search and library detail
templates. Replace them with `{% comment %}...{% endcomment %}` blocks
and add a note explaining the distinction.

mnemosyne/library/templates/library/library_detail.html

@@ -146,11 +146,14 @@
                     {% if results_reranked.reranker_used %}
                         <span class="badge badge-success">{{ results_reranked.reranker_model|default:"on" }}</span>
                     {% else %}
-                        {# The A/B page always requests rerank=True, so a
+                        {% comment %}
+                        The A/B page always requests rerank=True, so a
                         negative here is always a skip with a reason —
                         surface the reason in a tooltip so the user
-                           knows *why* the B side fell back to fusion
-                           order. #}
+                        knows *why* the B side fell back to fusion order.
+                        Django's ``{# #}`` comment is single-line only;
+                        multi-line blocks must use ``{% comment %}``.
+                        {% endcomment %}
                         <span class="badge badge-warning"
                               title="{{ results_reranked.reranker_skip_reason|default:'unknown' }}">
                             unavailable

mnemosyne/library/templates/library/search.html

@@ -81,13 +81,17 @@
         <div class="stat">
             <div class="stat-title">Re-ranked</div>
             <div class="stat-value text-lg">
-                {# Three-state indicator:
+                {% comment %}
+                Three-state indicator:
                   - Yes: re-ranker ran successfully
                   - Skipped (+ tooltip): re-rank was requested but the
                     pipeline bailed — badge colour is a warning so the
                     user knows something didn't work
                   - Off: user unchecked the re-rank box
-                #}
+                Note: Django's ``{# #}`` comment is single-line only;
+                multi-line blocks must use ``{% comment %}`` or they
+                render as literal text.
+                {% endcomment %}
                 {% if results.reranker_used %}
                     <span class="badge badge-success">Yes</span>
                 {% elif results.reranker_skip_reason %}