feat(examples): add PostgreSQL example with user relationship

Adds an example demonstrating user, comment, and follower relationship
including:
- User management with profiles
- Comments (not really useful, just for showcasing)
- Follower/follozing relationships
- Ineractive CLI interface with CRUD operations
- Database migrations for the example schema

migrations/20250605215127_users-comments-and-followers.down.sql

@@ -0,0 +1,4 @@
+DROP TABLE IF EXISTS Followers;
+DROP TABLE IF EXISTS Comments;
+DROP TABLE IF EXISTS Profiles;
+DROP TABLE IF EXISTS Users;

migrations/20250605215127_users-comments-and-followers.up.sql

@@ -0,0 +1,30 @@
+-- Add migration script here
+CREATE TABLE Users (
+  id SERIAL PRIMARY KEY,
+  username VARCHAR(100) UNIQUE NOT NULL
+);
+
+CREATE TABLE Profiles (
+  id SERIAL PRIMARY KEY,
+  user_id INT UNIQUE NOT NULL,
+  bio TEXT,
+  display_name VARCHAR(100),
+  FOREIGN KEY (user_id) REFERENCES Users(id)
+);
+
+CREATE TABLE Comments (
+  id SERIAL PRIMARY KEY,
+  author_id INT NOT NULL,
+  content TEXT NOT NULL,
+  FOREIGN KEY (author_id) REFERENCES Users(id)
+);
+
+CREATE TABLE Followers (
+  id SERIAL PRIMARY KEY,
+  followed INT NOT NULL,
+  follower INT NOT NULL,
+  FOREIGN KEY (followed) REFERENCES Users(id) ON DELETE CASCADE,
+  FOREIGN KEY (follower) REFERENCES Users(id) ON DELETE CASCADE,
+  CHECK (followed != follower),
+  UNIQUE (followed, follower)
+);