docs: Add Flash documentation

[promptless]

Summary

Add comprehensive Flash documentation section to the Runpod docs site, covering the Python SDK for serverless AI workloads.

What is Flash?

Flash is a Python SDK that lets developers run @Endpoint decorated functions on Runpod Serverless GPUs/CPUs. Write local Python code, and Flash handles provisioning, scaling, and dependency management automatically.

Documentation Structure

Core Concepts

• Overview - Introduction to Flash and its capabilities
• Quickstart - Get running on a GPU in 5 minutes
• Endpoint functions - Queue-based and load-balanced endpoint patterns
• Execution model - How Flash executes code remotely
• Custom Docker images - Deploy pre-built images (vLLM, etc.)
• Pricing - Cost information and optimization tips
• Troubleshooting - Common issues and solutions

Flash Apps

• Overview - What Flash apps are and when to use them
• Build app - Tutorial for creating your first app
• Initialize project - flash init and project structure
• Local testing - flash run development server
• Deploy apps - flash deploy to production
• Customize app - Advanced configuration
• Apps and environments - Managing dev/staging/prod
• Requests - Making requests to deployed apps

CLI Reference

• Overview - CLI command summary
• login - Authentication
• init - Project initialization
• run - Development server
• build - Build artifacts
• deploy - Production deployment
• undeploy - Remove endpoints
• env - Environment management
• app - App management

Configuration

• Parameters - All Endpoint class parameters
• GPU types - Available GPU options (GpuGroup, GpuType)
• CPU types - Available CPU instances
• Storage - Network volumes
• Best practices - Performance and cost optimization

Tutorials

• Image generation with SDXL - GPU-accelerated Stable Diffusion
• Text generation with Transformers - Deploy language models
• Build a REST API - Load-balanced HTTP endpoints

Files Changed

Category	Files	Lines Added
Flash core docs	12	~2,800
Flash apps	8	~2,100
Flash CLI	8	~1,500
Flash configuration	5	~1,150
Flash tutorials	3	~1,840
Navigation (docs.json)	1	~60
Total	33	~8,500

Additional Changes

• Updated docs.json navigation to include Flash section
• Added CSS styles for overview page layouts
• Updated tooltips for Flash-related concepts
• Minor updates to related pages (Serverless overview, tutorials introduction)

Testing

• Verified all internal links resolve correctly
• Tested code samples from quickstart and tutorials against live Flash SDK
• Confirmed navigation structure renders properly in Mintlify