Add redirect support, live candidate list, per-article save count, and error pages

- Detect redirect targets (e.g. "handling stolen goods" → "Possession of
  stolen goods") and use piped links [[target|title]] in edits; exclude
  articles already linking to the redirect target from candidates
- Remove candidates from the list in real time as they are checked and
  found invalid, with live count update in the summary
- Track and display per-article save count in the stats line
- Rename "Find Link" to "Missing Link" throughout
- Show redirect target in the article heading
- Report save errors to the user via error page instead of crashing
- Filter self-links using case-insensitive first-letter comparison

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/article.html

@@ -18,11 +18,17 @@
   <div class="d-flex flex-wrap align-items-baseline gap-3 mb-1">
     <h1 class="h4 mb-0">Find links to "{{ title }}"</h1>
     <a href="https://en.wikipedia.org/wiki/{{ title }}" target="_blank" class="text-muted small">{{ title }} ↗</a>
+    {% if redirect_to %}
+    <span class="text-muted small">→ redirects to <a href="https://en.wikipedia.org/wiki/{{ redirect_to }}" target="_blank">{{ redirect_to }} ↗</a></span>
+    {% endif %}
   </div>
 
   <div class="d-flex gap-3 mb-3 text-muted small">
     <span>{{ total }} mentions total</span>
     <span>{{ with_link }} already linked ({{ "{:.0%}".format(with_link / total) }})</span>
+    {% if saves_this_session %}
+    <span class="text-success">{{ saves_this_session }} added this session</span>
+    {% endif %}
   </div>
 
   <div id="search-progress" class="my-4">
@@ -57,11 +63,11 @@
   </div>
 
   {% if hits %}
-  <details class="border rounded p-3 mt-2">
-    <summary class="text-muted small" style="cursor:pointer">{{ hits | length }} candidates</summary>
-    <ol class="mt-3 mb-0 small">
+  <details id="candidates-section" class="border rounded p-3 mt-2">
+    <summary class="text-muted small" style="cursor:pointer"><span id="candidates-count">{{ hits | length }}</span> candidates</summary>
+    <ol class="mt-3 mb-0 small" id="candidates-list">
     {% for hit in hits %}
-      <li class="mb-1">
+      <li class="mb-1" data-title="{{ hit.title }}">
         <a href="{{ url_for("article_page", url_title=url_title, title=hit.title) }}">{{ hit.title }}</a>
       </li>
     {% endfor %}
@@ -76,6 +82,7 @@
 (function () {
   const hits = {{ hits | map(attribute='title') | list | tojson }};
   const linkTo = {{ title | tojson }};
+  const redirectTo = {{ redirect_to | tojson }};
   const apiUrl = {{ url_for('api_valid_hit') | tojson }};
   const pageUrl = new URL(window.location.href);
 
@@ -83,6 +90,16 @@
   const elStatus   = document.getElementById('search-status');
   const elResult   = document.getElementById('result');
   const elAllDone  = document.getElementById('all-done');
+  const elList     = document.getElementById('candidates-list');
+
+  function removeCandidate(title) {
+    if (!elList) return;
+    const li = elList.querySelector(`li[data-title="${CSS.escape(title)}"]`);
+    if (!li) return;
+    li.remove();
+    const elCount = document.getElementById('candidates-count');
+    if (elCount) elCount.textContent = elList.children.length;
+  }
 
   async function search() {
     for (const hitTitle of hits) {
@@ -91,6 +108,7 @@
       let data;
       try {
         const params = new URLSearchParams({ link_to: linkTo, link_from: hitTitle });
+        if (redirectTo) params.append('redirect_to', redirectTo);
         const resp = await fetch(apiUrl + '?' + params);
         if (!resp.ok) continue;
         data = await resp.json();
@@ -98,7 +116,7 @@
         continue;
       }
 
-      if (!data.valid) continue;
+      if (!data.valid) { removeCandidate(hitTitle); continue; }
 
       elProgress.hidden = true;
 
@@ -123,6 +141,8 @@
     }
 
     elProgress.hidden = true;
+    const elCandidates = document.getElementById('candidates-section');
+    if (elCandidates) elCandidates.hidden = true;
     elAllDone.hidden = false;
   }