Issue Description

Add a project roadmap document to satisfy the OpenSSF Best Practices Badge Silver criterion documentation_roadmap.

OSSF Silver requires: "The project MUST have a documented roadmap that describes what the project intends to do and not do for at least the next year."

Add ROADMAP.md to repository root with:

• 12-18 month horizon (Q1 2026 through Q1 2027)
• Six priority areas: Agent Framework, Instructions, Prompts, Enterprise Readiness, Documentation, Community
• Explicit "Will Do" and "Won't Do" sections for each area
• Out of Scope section defining project boundaries
• Success metrics table
• Timeline overview
• Community influence process

Additional Context

Additional OSSF Silver gaps identified during research:

• Missing GOVERNANCE.md (governance, roles_responsibilities criteria)
• Missing architecture documentation (documentation_architecture criterion)
• Missing threat model (documentation_security criterion)