Guard profile.did usage and fix related bugs

Add null checks and early returns in Handle to avoid using an undefined
profile.did. Add profile.data?.did to effect deps and use "" fallbacks
when checking Set membership. Fix useActorCompatibilityQuery type
(undefined) and remove unused LabelMedium import. Use empty-string
fallback when calling useFollowersInfiniteQuery.

apps/web/src/components/Handle/Handle.tsx

···
       setIsSignInOpen(true);
       return;
     }
+    if (!profile.data?.did) {
+      return;
+    }
     setFollows((prev) => new Set(prev).add(profile.data?.did));
     followAccount(profile.data?.did);
   };
···
       setIsSignInOpen(true);
       return;
     }
+    if (!profile.data?.did) {
+      return;
+    }
+
     setFollows((prev) => {
+      if (!profile.data?.did) {
+        return prev;
+      }
       const newSet = new Set(prev);
       newSet.delete(profile.data?.did);
       return newSet;
···
     }
     setFollows((prev) => {
       const newSet = new Set(prev);
+      if (!profile.data?.did) {
+        return newSet;
+      }
       if (
         data.followers.some(
           (follower: { did: string }) => follower.did === currentDid,
···
       }
       return newSet;
     });
-  }, [data, isLoading]);
+  }, [data, isLoading, currentDid, setFollows, profile.data?.did]);
 
   useEffect(() => {
     if (profile.isLoading || profile.isError) {
···
               {(profile.data?.did !== localStorage.getItem("did") ||
                 !localStorage.getItem("did")) && (
                 <div className="ml-auto mt-[10px]">
-                  {!follows.has(profile.data?.did) && !isLoading && (
+                  {!follows.has(profile.data?.did || "") && !isLoading && (
                     <Button
                       shape="pill"
                       size="mini"
···
                       Follow
                     </Button>
                   )}
-                  {follows.has(profile.data?.did) && !isLoading && (
+                  {follows.has(profile.data?.did || "") && !isLoading && (
                     <Button
                       shape="pill"
                       size="mini"

apps/web/src/components/Stats/Stats.tsx

···
 import { css } from "@emotion/react";
 import styled from "@emotion/styled";
-import { HeadingSmall, LabelMedium } from "baseui/typography";
+import { HeadingSmall } from "baseui/typography";
 import numeral from "numeral";
 
 const Group = styled.div<{ mb?: number }>`

apps/web/src/hooks/useProfile.tsx

···
     enabled: !!did,
   });
 
-export const useActorCompatibilityQuery = (did: string | undefine) =>
+export const useActorCompatibilityQuery = (did: string | undefined) =>
   useQuery({
     queryKey: ["profile", "compatibility", did],
     queryFn: () => getActorCompatibility(did!),

apps/web/src/pages/profile/followers/Followers.tsx

···
   const { did } = useParams({ strict: false });
   const profile = useProfileByDidQuery(did!);
   const { data, fetchNextPage, hasNextPage, isFetchingNextPage } =
-    useFollowersInfiniteQuery(profile.data?.did, 20);
+    useFollowersInfiniteQuery(profile.data?.did || "", 20);
   const { mutate: followAccount } = useFollowAccountMutation();
   const { mutate: unfollowAccount } = useUnfollowAccountMutation();