Replace emoji icons with a monochrome SVG icon set

Emoji (📚 🔖 🏷️ ✎ ✕ 🕓 ⏳ 🤖 ⚠️ 🔍) rendered in each platform's own
colorful style and looked inconsistent. Add app/templates/_icons.html
with small inline SVG macros (Lucide-style, MIT-licensed path data,
stroke=currentColor) and use them throughout instead, so icons pick
up the muted/accent text colors like the rest of the UI.

The needs-review bookmark toggle now uses an outline vs. filled icon
for its two states instead of swapping emoji.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/templates/_link_card_edit.html

@@ -1,3 +1,4 @@
+{% import "_icons.html" as icons %}
 <div class="panel link-card" id="link-{{ link.id }}">
   <form hx-put="/links/{{ link.id }}" hx-target="#link-{{ link.id }}" hx-swap="outerHTML"
         hx-disabled-elt="button">
@@ -5,7 +6,7 @@
       {{ link.url }}
     </div>
     <div class="muted" style="font-size:.75rem; margin:3px 0 10px;">
-      🕓 hinzugefügt am {{ link.created_at | datum }}
+      {{ icons.clock(size=13) }} hinzugefügt am {{ link.created_at | datum }}
     </div>
 
     <div class="field">
@@ -59,7 +60,8 @@
               hx-swap="outerHTML"
               hx-disabled-elt="this"
               hx-confirm="Link erneut laden und von der KI neu beschreiben lassen? Bestehende Angaben werden dabei ersetzt.">
-        <span class="htmx-indicator">⏳</span> 🤖 KI neu beschreiben lassen
+        <span class="htmx-indicator icon-spin">{{ icons.spinner(size=14) }}</span>
+        {{ icons.sparkles(size=14) }} KI neu beschreiben lassen
       </button>
       {% endif %}
     </div>