README rewrite — lead with zero-token git and June 1 credit-saving angle

[canoo]

Problem

The current README leads with 'tool-agnostic framework for multi-model agentic orchestration' — accurate but abstract. It doesn't answer 'why should I install this right now?' within the first scroll.

Context

GitHub AI Credits move to token-based billing June 1, 2026. Developers are actively searching for complexity-based routing to preserve cloud credits for hard problems. NEXUS's local routing is the direct answer, and the 'zero-token git' workflow (routing commit messages, lint fixes, boilerplate to local Ollama) is the most concrete cited use case in the community (r/ClaudeCode, April 2026).

What needs updating

1. Tagline — lead with the concrete value: route boilerplate locally, save cloud credits for what matters
2. Problem section — the configuration wall: developers copy-paste their 'soul' between tools (r/LocalLLaMA, r/ChatGPTCoding, April 2026)
3. Feature list — clear, structured with what's built now vs. what's on the roadmap
4. Tool compatibility matrix — table showing all supported tools and support level
5. Zero-token git section — concrete example of the local routing workflow
6. Research references — cite community findings for credibility
7. Roadmap table — milestone sequence with dependency notes
8. Architecture diagram — update to reflect multi-tool projection model

Dependencies

Can be partially done now (current features). Full update after #86 (compat matrix) so the tool support table is accurate.