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.

.agents/notes/implemented/architecture/2026-06-21-mandatory-app-attribution-headers.md

@@ -51,7 +51,7 @@ Endpoint detection is not part of this Agent Note because no endpoint-specific m
 
 The landed contract:
 
-- `dsh-llm` documents the mandatory `User-Agent` attribution contract for `LlmAdapter` authors (`LlmAdapter` JSDoc, package README, and the adapter-contract section of `docs/core-data-structures/llm-streaming.md`).
+- `dsh-llm` documents the mandatory `User-Agent` attribution contract for `LlmAdapter` authors (`LlmAdapter` JSDoc, package README, and the adapter-contract section of `docs/subsystems/llm-streaming.md`).
 - A shared helper (`attributionHeaders` / `userAgent`) constructs the app identity and the standard `User-Agent` value from package metadata, so adapters do not hand-copy version constants.
 - `dsh-llm-deepseek` sends the shared `User-Agent` on every request and its mock-server suite asserts the exact value.
 - `dsh-llm-pi-ai` sends the same `User-Agent` through pi-ai's `StreamOptions.headers` hook and its mock-server suite asserts the exact value.