Add nested posts UI cutover.

Render reply trees with permission-aware inline controls, and move hunt, profile, voting, submission, and hiding flows to post storage.

schema.sql

@@ -63,6 +63,9 @@ CREATE TABLE IF NOT EXISTS posts (
 CREATE INDEX IF NOT EXISTS idx_posts_parent_created
   ON posts(parent_id, created_at, id);
 
+CREATE INDEX IF NOT EXISTS idx_posts_author_created
+  ON posts(author_id, created_at DESC, id DESC);
+
 CREATE INDEX IF NOT EXISTS idx_posts_root_date
   ON posts(post_date, post_state)
   WHERE parent_id IS NULL;