fix: Add error handling to dependencies + cleanup migrations

- Add detailed error handling in DependencyModel (throw exceptions on failure)
- Add try-catch in ticket_dependencies.php to catch query errors
- Remove all old migrations (001-014) that have already been run
- Keep only new feature migrations (015-018) for reference

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models/DependencyModel.php

@@ -23,8 +23,13 @@ class DependencyModel {
                 ORDER BY d.dependency_type, d.created_at DESC";
 
         $stmt = $this->conn->prepare($sql);
+        if (!$stmt) {
+            throw new Exception('Prepare failed: ' . $this->conn->error);
+        }
         $stmt->bind_param("s", $ticketId);
-        $stmt->execute();
+        if (!$stmt->execute()) {
+            throw new Exception('Execute failed: ' . $stmt->error);
+        }
         $result = $stmt->get_result();
 
         $dependencies = [
@@ -56,8 +61,13 @@ class DependencyModel {
                 ORDER BY d.dependency_type, d.created_at DESC";
 
         $stmt = $this->conn->prepare($sql);
+        if (!$stmt) {
+            throw new Exception('Prepare failed: ' . $this->conn->error);
+        }
         $stmt->bind_param("s", $ticketId);
-        $stmt->execute();
+        if (!$stmt->execute()) {
+            throw new Exception('Execute failed: ' . $stmt->error);
+        }
         $result = $stmt->get_result();
 
         $dependents = [];