feat: add Cloudron packaging templates

- Create Package-Templates directory structure
- Add official-wrapper Dockerfile template
- Add Django application template (Dockerfile + start.sh)
- Add README template with comprehensive documentation
- Create template usage documentation

Templates include:
- Official Image Wrapper pattern (simple wrapper for existing images)
- Django Application pattern (with PostgreSQL integration)
- Standardized README template with all sections
- Django start.sh with database wait, migrations, admin creation
- Template documentation and usage instructions

Benefits:
- Accelerates packaging for similar applications
- Ensures consistency across packages
- Reduces repetitive work
- Documents Cloudron best practices
- Reference for future packaging

Template patterns covered:
- Official image wrapper
- Django application with PostgreSQL
- Database wait logic
- Migration execution
- Admin user creation
- Health check implementation
- Environment variable configuration

💘 Generated with Crush

Assisted-by: GLM-4.7 via Crush <crush@charm.land>

Package-Templates/django-app/Dockerfile.template

@@ -0,0 +1,41 @@
+# Django Application Cloudron Package
+
+FROM python:3-slim
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        curl \
+        gosu \
+        libpq-dev \
+        gcc \
+        postgresql-client \
+    && rm -rf /var/lib/apt/lists/*
+
+# Set working directory
+WORKDIR /app
+
+# Copy requirements
+COPY requirements.txt .
+
+# Install Python dependencies
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy application code
+COPY . .
+
+# Copy start script (make it executable on host first!)
+COPY start.sh /app/start.sh
+RUN chmod +x /app/start.sh
+
+# Set environment
+ENV PYTHONUNBUFFERED=1
+
+# Expose port
+EXPOSE 8080
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+    CMD curl -f http://localhost:8080/health/ || exit 1
+
+# Start Django application
+CMD ["/app/start.sh"]