feat: add project bulk download and bulk video delete

Add a "Download project" / "Download selected" flow that builds a
server-side manifest of downloadable media, plus a selection mode with
bulk delete for project videos.

Gate viewer downloads behind a new project allowDownloads setting
(default off, opt-in). Admins can always download; enabling on a public
project allows anonymous visitors to download. Enforce the setting on
every download surface (manifest, version, asset, watch, video routes)
via canDownloadProjectMedia.

Add rate limits for the manifest endpoint, host allowlisting for direct
download URLs, and configurable file/byte caps.

Closes #16
Closes #19

app/(dashboard)/projects/[projectId]/share/project-share-page-client.tsx

@@ -38,6 +38,7 @@ interface ProjectSharePageProps {
 export default function ProjectSharePageClient({ projectId }: ProjectSharePageProps) {
   const [projectName, setProjectName] = useState('');
   const [projectVisibility, setProjectVisibility] = useState('');
+  const [allowDownloads, setAllowDownloads] = useState(false);
   const [isLoading, setIsLoading] = useState(true);
   const [members, setMembers] = useState<ProjectMember[]>([]);
   const [copied, setCopied] = useState(false);
@@ -56,6 +57,7 @@ export default function ProjectSharePageClient({ projectId }: ProjectSharePagePr
           const project = data.data;
           setProjectName(project.name || '');
           setProjectVisibility(project.visibility || 'PRIVATE');
+          setAllowDownloads(project.allowDownloads ?? false);
           setMembers(project.members || []);
         }
       })
@@ -174,6 +176,14 @@ export default function ProjectSharePageClient({ projectId }: ProjectSharePagePr
                 <div className="flex-1">
                   <div className="font-medium">{visibilityInfo.title}</div>
                   <div className="text-sm opacity-80">{visibilityInfo.description}</div>
+                  {(projectVisibility === 'PUBLIC' || projectVisibility === 'INVITE') && (
+                    <div className="text-sm opacity-80 mt-1">
+                      Viewer downloads:{' '}
+                      {allowDownloads
+                        ? 'enabled (includes anonymous visitors on public links)'
+                        : 'disabled'}
+                    </div>
+                  )}
                 </div>
                 <Link href={`/projects/${projectId}/settings`}>
                   <Button variant="ghost" size="sm" className="text-current hover:bg-current/10">