docs: rename core-data-structures/ to subsystems/

The folder is becoming the home of one-doc-per-subsystem pages (intro +
data structures + cordis services/events), so the name must describe the
whole contract, not just the type-vocabulary third of it. Mechanical
rename rebuilt on current master: every inbound Markdown link, generator
constant, website route, type-equiv manifest path, and spec expectation
moves together; the zh sides of the notes whose prose names the folder
are aligned (子系统) in the same change; touched bilingual pairs
re-recorded; translation-prompt snapshot re-recorded (its example embeds
development.md). Historical Agent Note slugs keep their dated
filenames.

packages/subprocess/subprocess/README.md

@@ -15,7 +15,7 @@ The subprocess seam (`ctx.subprocess`) is the process half of one execution worl
 - `scrubbedParentEnv()` / `SENSITIVE_ENV_PATTERN` are the one shared scrub definition: ambient credential-shaped and `DSH_*` names are dropped, and explicit `env` merges after the scrub. The local ordinary and terminal spawns both apply it; SDK-managed transports that own their spawn may import it directly.
 - Disposal of the service terminates all still-running managed processes and awaits their exit.
 
-See the [subprocess data-structure catalog](../../../docs/core-data-structures/subprocess.md) and the [seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-26-subprocess-seam.md).
+See the [subprocess data-structure catalog](../../../docs/subsystems/subprocess.md) and the [seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-26-subprocess-seam.md).
 
 ## Model Experience