feat: add copyright report UI (public report page, admin flag button, sysadmin review)

- /report: public three-step page to find a broadcaster, pick an asset, and
  submit a DMCA-style claim; uses asset.url fallback for images without previews
- Admin console: flag button opens report modal for the selected asset
- Settings page: sysadmin copyright reports section with status/broadcaster
  filters, paginated table, and review modal with action radio buttons
- Footer on index.html links to /report

src/main/resources/static/js/admin/console.js

@@ -77,6 +77,7 @@ export function createAdminConsole({
     const selectedEditBtn = document.getElementById("selected-asset-edit");
     const selectedVisibilityBtn = document.getElementById("selected-asset-visibility");
     const selectedDeleteBtn = document.getElementById("selected-asset-delete");
+    const selectedReportBtn = document.getElementById("selected-asset-report");
     const assetActionRow = document.getElementById("asset-actions");
     const assetActionButtons = Array.from(assetActionRow?.querySelectorAll("button") ?? []);
     const canvasResolutionLabel = document.getElementById("canvas-resolution");
@@ -2185,6 +2186,9 @@ export function createAdminConsole({
             selectedDeleteBtn.disabled = !asset;
             selectedDeleteBtn.title = asset ? "Delete asset" : "Delete asset";
         }
+        if (selectedReportBtn) {
+            selectedReportBtn.disabled = !asset;
+        }
     }
 
     function ensureDurationMetadata(asset) {