feat: install and configure OpenSpec for spec-driven development

- Add openspec/ directory with AGENTS.md and project.md
- Add root AGENTS.md stub for AI assistants
- Create Claude Code slash commands:
  - /openspec:proposal - Create change proposals
  - /openspec:apply - Implement changes
  - /openspec:archive - Archive completed changes
- Configure project.md with ROI Theme conventions and architecture

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

AGENTS.md

@@ -0,0 +1,18 @@
+<!-- OPENSPEC:START -->
+# OpenSpec Instructions
+
+These instructions are for AI assistants working in this project.
+
+Always open `@/openspec/AGENTS.md` when the request:
+- Mentions planning or proposals (words like proposal, spec, change, plan)
+- Introduces new capabilities, breaking changes, architecture shifts, or big performance/security work
+- Sounds ambiguous and you need the authoritative spec before coding
+
+Use `@/openspec/AGENTS.md` to learn:
+- How to create and apply change proposals
+- Spec format and conventions
+- Project structure and guidelines
+
+Keep this managed block so 'openspec update' can refresh the instructions.
+
+<!-- OPENSPEC:END -->