Document AGENTS memory in config guide

[w287346141]

Summary

• update the configuration guide memory copy to mention AGENTS.md alongside CARBON.md project rules
• replace the old single ~/.carboncode/memory.md example with the current ~/.carboncode/memory/ entry layout
• keep the static guide HTML and translation copy in sync

Validation

• npm.cmd test -- --run tests/carbon-productization.test.ts tests/docs-homepage-style.test.ts
• npm run verify