Add user follows to following feed

db/migrations/23_followed_users.sql

@@ -0,0 +1,10 @@
+CREATE TABLE IF NOT EXISTS followed_users (
+    follower_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    followed_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (follower_id, followed_id),
+    CHECK (follower_id <> followed_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_followed_users_followed
+    ON followed_users(followed_id, follower_id);