[codex] Layer Summon terminology across docs and demos

[nahiyankhan]

Summary

• Reframe the public adoption docs around the simpler adopter vocabulary: surface, host tool, sandbox, surface config, and diagnostics.
• Update the demo/workbench and surface gallery visible copy so first-run UI labels match the new terminology layer.
• Keep runtime symbols, protocol paths, public APIs, package exports, and internal type names unchanged.

Validation

• pnpm check:public-api
• pnpm check:public-packages
• pnpm test
• pnpm typecheck
• pnpm test:gallery