docs: charter meta-framework vision, research, and SAND-WP-0002

Rewrite INTENT.md as the sand-boxer meta-framework charter (OpenRouter-style
sandbox API, extensions, payments, Coulomb sibling boundaries). Add research
under research/, update SCOPE.md, bootstrap workplans SAND-WP-0001/0002, and
State Hub integration files from the bootstrap pass.

.claude/rules/architecture.md

@@ -0,0 +1,8 @@
+## Architecture
+
+<!-- TODO: Describe the key design decisions and component structure.
+     Key modules, data flows, external integrations, state machines, etc. -->
+
+## Quick Reference
+
+`~/state-hub/mcp_server/TOOLS.md` — MCP tool reference