Fix follower handling

src/main/resources/db/migration/V8__add_remote_actor_uri_to_follows.sql

@@ -0,0 +1,19 @@
+-- Migration V8: Add remote_actor_uri column to follows table
+
+-- Add the column
+ALTER TABLE follows ADD COLUMN remote_actor_uri VARCHAR(512);
+
+-- Add index for remote_actor_uri
+CREATE INDEX idx_follows_remote_actor_uri ON follows(remote_actor_uri) WHERE remote_actor_uri IS NOT NULL;
+
+-- Update the constraint to allow either follower_id OR remote_actor_uri
+ALTER TABLE follows ALTER COLUMN follower_id DROP NOT NULL;
+
+-- Add check constraint to ensure either follower_id or remote_actor_uri is set (but not both)
+ALTER TABLE follows ADD CONSTRAINT chk_follows_actor CHECK (
+    (follower_id IS NOT NULL AND remote_actor_uri IS NULL) OR
+    (follower_id IS NULL AND remote_actor_uri IS NOT NULL)
+);
+
+-- Add comment for documentation
+COMMENT ON COLUMN follows.remote_actor_uri IS 'Remote ActivityPub actor URI for remote-to-local follows (null if local follower)';