feat(upload): add file upload UI — avatar, editor paste/drop, attachments

- Add uploadFile method to ApiClient (FormData + 401 handling)
- Add useFileUpload hook with client-side validation
- ActorAvatar renders actual avatar images with fallback to initials
- Account settings: replace URL input with clickable avatar upload
- RichTextEditor: add Image extension, paste/drop/insertFile support
- Markdown renderer: add img component for uploaded images
- CommentInput & ReplyInput: add paperclip button for file attachments
- Issue description: paste/drop file upload support

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/features/workspace/hooks.ts

@@ -32,5 +32,11 @@ export function useActorName() {
       .slice(0, 2);
   };
 
-  return { getMemberName, getAgentName, getActorName, getActorInitials };
+  const getActorAvatarUrl = (type: string, id: string): string | null => {
+    if (type === "member") return members.find((m) => m.user_id === id)?.avatar_url ?? null;
+    if (type === "agent") return agents.find((a) => a.id === id)?.avatar_url ?? null;
+    return null;
+  };
+
+  return { getMemberName, getAgentName, getActorName, getActorInitials, getActorAvatarUrl };
 }