fix(v1-endpoint): Host API calls were scoped by run

[cmath10]

Summary

• add an optional host API scope to each endpoint run
• route Pinia context and Host API calls through run-scoped RPC method names
• preserve the existing unscoped endpoint behavior for current consumers
• cover simultaneous runs with different host locations

Checks

• corepack yarn workspace @retailcrm/embed-ui-v1-endpoint test tests/endpoint.test.ts
• corepack yarn test:typecheck
• corepack yarn eslint packages/v1-endpoint/src/common.ts packages/v1-endpoint/src/common/extension.ts packages/v1-endpoint/src/remote/endpoint.ts packages/v1-endpoint/tests/endpoint.test.ts
• corepack yarn workspaces foreach -A --topological-dev run build