Improve ORBIT branding and LLM routing discoverability

[AIGNLAI]

Summary

• Keep the repository name ORBIT and its canonical URL unchanged.
• Add the README H1: ORBIT: A Unified Toolbox for LLM Routing.
• Put the existing FCS DOI link near the top, and strengthen the introduction with natural LLM routing, model routing, cost-aware inference, and routing benchmark terminology.
• Document the full-name-first convention for future papers, project introductions, and related open-source method documentation.
• Preserve the existing published paper title and BibTeX rather than retroactively renaming the publication.

Repository metadata (already applied separately)

Description now starts with ORBIT: A Unified Toolbox for LLM Routing and describes unified routing, cost-aware inference, multimodal benchmarks, and reproducible evaluation.
Added topics: llm-routing, model-routing, llm-router, llm-routing-benchmark, llm-evaluation, cost-aware-routing, large-language-models. All seven existing topics were retained. Repository name, URL, and other settings are unchanged.

Validation

• README has exactly one H1 with the requested full name.
• Existing external URLs and the complete citation section are preserved.
• Table-of-contents anchors resolve and local image paths exist.
• git diff --check passed; no runtime code or configs changed.

These changes improve keyword association and project consistency; they do not guarantee immediate search-index refresh or ranking improvements.