Backend: PDO models base class and query helpers

[Manak-hash]

Description

Build a lightweight base Model class using PDO to standardize database queries across all controllers. This avoids repeating boilerplate PDO code in every controller and makes the backend easier to maintain.

Tasks

• Create models/Model.php — base class with:
  • Static db() method returning the PDO instance from config/database.php
  • findById($table, $id) helper
  • findAll($table, $conditions, $params) helper
  • insert($table, $data) — returns last insert ID
  • update($table, $data, $where, $params) helper
  • delete($table, $where, $params) helper
  • All queries use prepared statements
• Create individual model classes that extend base:
  • models/User.php
  • models/Project.php
  • models/Application.php
  • models/Skill.php
  • models/Notification.php
  • models/Bookmark.php
• Each model has domain-specific methods (e.g. Project::findBySlug(), User::findByEmail())
• Create helpers/Validator.php with reusable validation helpers:
  • required($fields, $data)
  • email($value)
  • minLength($value, $min)
  • inArray($value, $allowed)

Acceptance Criteria

• All models extend base Model
• No raw SQL strings outside of model files
• All queries use prepared statements (no string interpolation)
• Validator helpers work correctly for common field types