Add nested posts UI (#5)

## Summary
- Cut hunt, question, submission, voting, hiding, and profile flows over to unified posts
- Render nested replies with permission-aware inline Reply/Edit controls and edited markers
- Add post profile queries and the author index migration they depend on

Co-authored-by: codegirl-007 <s.raide@gmail.com>

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;