add action output and replace it in assert

[fantazista]

Runner (dtc/src/index.ts)

Tracks per-phase results in ctx.output (arrange, act, assert, clean).
Passes a 4th arg to plugins: output (same object), so assert can read output.act.
Export: export * from './domain.js' instead of export type *.
resolveOutputRefs (dtc/src/utils.ts)

Resolves @output.* strings against the given object (with output.data fallback).
Plugins

HTTP assert (http-call-plugin.ts): resolves assert args with resolveOutputRefs(..., output?.act) before checks.
RDS (rds-data-plugin.ts): same for assert; arrange/clean run statements sequentially; strip response before executeStatement.
Tests

index.test.ts: only assert first 3 mock args so the new 4th param does not break expectations.
Docs

README.md: build / test commands for the monorepo.