Optimize scan process with quick/deep modes and archive tag merging

Quick scan (default):
- Pre-load all ImportTask records for O(1) duplicate checks
- Batch task creation commits (50 at a time)
- Cache import settings (5-min TTL)
- Skip pHash comparison for speed

Deep scan (on-demand):
- Full reprocessing of all files
- pHash similarity detection
- Optional thumbnail regeneration
- Optional sidecar re-application

Archive tag merging:
- Add archive tags to existing images when duplicates found
- Works for both hash and pHash duplicate detection

Also fixes:
- Add missing source/post tag icons to gallery templates

app/static/js/bulk-select.js

@@ -555,11 +555,13 @@
         item.appendChild(overlay);
       }
 
-      // Render tags
+      // Render tags with icons
       overlay.innerHTML = visibleTags.map(t => {
         const displayName = getTagDisplayName(t.name, t.kind);
+        const icon = getTagIcon(t.kind);
         const encodedName = encodeURIComponent(t.name);
-        return `<a class="tag-chip" href="/gallery?tag=${encodedName}" title="Filter by ${escapeHtml(t.name)}" onclick="event.stopPropagation()">${escapeHtml(displayName)}</a>`;
+        const prefix = icon !== '#' ? icon + ' ' : '#';
+        return `<a class="tag-chip" href="/gallery?tag=${encodedName}" title="Filter by ${escapeHtml(t.name)}" onclick="event.stopPropagation()">${prefix}${escapeHtml(displayName)}</a>`;
       }).join('');
 
     } catch (e) {

app/static/js/gallery-infinite.js

@@ -187,6 +187,21 @@
     return section;
   }
 
+  // Tag icon mapping (matches showcase.js and bulk-select.js)
+  function getTagIcon(kind) {
+    const icons = {
+      artist: '🎨',
+      archive: '🗜️',
+      character: '👤',
+      series: '📺',
+      fandom: '🎭',
+      rating: '⚠️',
+      source: '🌐',
+      post: '📌'
+    };
+    return icons[kind] || '#';
+  }
+
   // Create a single image element
   function createImageElement(img) {
     const item = document.createElement('div');
@@ -196,12 +211,13 @@
     item.dataset.type = img.is_video ? 'video' : 'image';
     item.dataset.filename = img.filename;
 
-    // Build tag overlay HTML
+    // Build tag overlay HTML with icons
     let tagsHtml = '';
     if (img.tags && img.tags.length > 0) {
       const tagChips = img.tags.map(t => {
         const displayName = t.name.includes(':') ? t.name.split(':')[1] : t.name;
-        const prefix = t.kind === 'user' ? '#' : '';
+        const icon = getTagIcon(t.kind);
+        const prefix = icon !== '#' ? icon + ' ' : '#';
         return `<a class="tag-chip" href="/gallery?tag=${encodeURIComponent(t.name)}" title="Filter by ${t.name}" onclick="event.stopPropagation()">${prefix}${displayName}</a>`;
       }).join('');
       tagsHtml = `<div class="tag-overlay">${tagChips}</div>`;