Initial commit: Clean Mold Cost Calculator application

- Flask-based mold cost calculation application
- PostgreSQL database with SQLAlchemy ORM
- Docker/Podman containerization
- Comprehensive documentation in docs/
- Clean, organized codebase without obsolete files
- Production-ready deployment configuration
- Enhanced pytest configuration with coverage reporting
- Master/Development branch structure

app/templates/error.html

@@ -0,0 +1,30 @@
+{% extends "base.html" %}
+
+{% block content %}
+<div class="container mt-5">
+    <div class="row justify-content-center">
+        <div class="col-md-8">
+            <div class="card">
+                <div class="card-header bg-danger text-white">
+                    <h4 class="mb-0">Error {{ code }}</h4>
+                </div>
+                <div class="card-body">
+                    <h5 class="card-title">{{ message }}</h5>
+                    <p class="card-text">
+                        {% if code == 404 %}
+                            The page you're looking for doesn't exist.
+                        {% elif code == 403 %}
+                            You don't have permission to access this resource.
+                        {% elif code == 400 %}
+                            The request was invalid.
+                        {% else %}
+                            An unexpected error occurred. Please try again later.
+                        {% endif %}
+                    </p>
+                    <a href="{{ url_for('main.home') }}" class="btn btn-primary">Return to Home</a>
+                </div>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}