Add comprehensive LLM4ChipDesign poster showcasing three research areas and featured submodules

[Copilot]

This PR adds a comprehensive poster for the LLM4Hardware repository titled "LLM4ChipDesign" that showcases the project's research contributions across three main areas and highlights featured submodules as requested.

What's Added

🎯 Main Poster Files

• LLM4ChipDesign_poster.pdf - High-resolution poster in PDF format (A1 size, 300 DPI)
• LLM4ChipDesign_poster.png - PNG version for web display and presentations
• create_poster.py - Python script for generating the poster using matplotlib
• POSTER_README.md - Comprehensive documentation explaining the poster contents

📊 Poster Structure

The poster is organized into three main research areas as specified:

1. LLM4Verilog Generation

• AutoChip: Functional Verilog from prompts
• VeriThoughts: Reasoning-based generation
• ROME: Hierarchical prompting
• Veritas: CNF-based synthesis
• PrefixLLM: Prefix circuit design

2. LLM4Security

• LLMPirate: IP piracy detection
• Security Assertions: LLM-generated SVA
• Hybrid-NL2SVA: Enhanced NL2SVA
• OpenTitan RAG: SVA for IP blocks

3. LLM4C2HLS

• C2HLSC: Software-to-hardware design gap bridging
• Automated C code refactoring
• HLS-compatible transformation
• Iterative LLM feedback mechanisms

🔧 Featured Submodules with Visual Demonstrations

The poster includes dedicated sections for the three featured submodules with workflow diagrams:

1. AutoChip - Shows the flow: Design Prompt → LLM → Functional Verilog
2. C2HLS - Demonstrates: C Code → LLM Processing → HLS-Ready C Code
3. Security Assertion Generation - Illustrates: Natural Language → LLM → SVA Code

🎨 Design Features

• Professional Layout: Clean, color-coded sections with consistent typography
• Visual Workflows: Simple diagrams showing the operation of each featured submodule
• Comprehensive Coverage: All major projects and research areas included
• Repository Information: Links to GitHub repo and project resources
• Key Features Section: Highlights framework capabilities and methodologies

The poster serves as an excellent overview for conferences, presentations, grant proposals, and research demonstrations, providing a comprehensive view of the LLM4Hardware project's scope and contributions.

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