feat(documents): migrate storage to filesystem, add server-side pagination

- Replace Base64 data URIs with file-based storage served via dedicated endpoints
- Add DocumentPreviewModal navigation, DocumentThumbnail fileUrl support
- Refactor documents page with server-side pagination, search, sort and filters
- Update all components to use fileUrl/downloadUrl instead of raw path
- Add pagination composable support (total, page, itemsPerPage, attachmentFilter)

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

app/composables/useSiteManagement.ts

@@ -23,6 +23,8 @@ type SiteDocument = {
   mimeType?: string
   size?: number
   path?: string
+  fileUrl?: string
+  downloadUrl?: string
 }
 
 type SiteWithDocuments = {
@@ -209,17 +211,23 @@ export function useSiteManagement() {
   }
 
   const downloadDocument = (doc: SiteDocument) => {
-    if (!doc?.path) return
+    if (doc?.downloadUrl) {
+      window.open(doc.downloadUrl, '_blank')
+      return
+    }
 
-    if (doc.path.startsWith('data:')) {
+    const url = doc?.fileUrl || doc?.path
+    if (!url) return
+
+    if (url.startsWith('data:')) {
       const link = document.createElement('a')
-      link.href = doc.path
+      link.href = url
       link.download = doc.filename || doc.name || 'document'
       link.click()
       return
     }
 
-    window.open(doc.path, '_blank')
+    window.open(url, '_blank')
   }
 
   const openPreview = (doc: SiteDocument) => {