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/errors/404.html

@@ -0,0 +1,14 @@
+{% extends "base.html" %}
+
+{% block title %}Not Found - MoldCost Pro{% endblock %}
+
+{% block content %}
+<div class="container mt-5">
+    <div class="text-center">
+        <h1 class="display-1">404</h1>
+        <h2 class="mb-4">Page Not Found</h2>
+        <p class="lead">The page you're looking for doesn't exist.</p>
+        <a href="{{ url_for('main.home') }}" class="btn btn-primary">Return Home</a>
+    </div>
+</div>
+{% endblock %}