docs: rebrand to GSD Core and restructure docs with Diataxis (#605)

* chore: wire docs/agents config into AGENTS.md Agent skills section

Add the `## Agent skills` discovery block pointing the engineering
skills at the existing docs/agents/{issue-tracker,triage-labels,domain}.md
files (issue tracker, triage label mapping, single-context domain docs).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* docs: rebrand to GSD Core and restructure docs with Diataxis

Reorganise the root README and docs/ around the Diataxis framework
(tutorials, how-to guides, reference, explanation), add new how-to
guides and schema references (STATE.md / CONTEXT.md / PLAN.md /
planning artifacts), and cross-link the whole set. Update the lone
legacy gsd-build reference to open-gsd; keep internal get-shit-done/
filesystem paths unchanged (directory rename tracked separately in
open-gsd/gsd-core#604). Regenerate the ja-JP, ko-KR, pt-BR and zh-CN
localised trees to mirror the new structure.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* docs: backfill changeset PR number (#605)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/CLI-TOOLS.md

@@ -1,6 +1,6 @@
 # GSD CLI Tools Reference
 
-> Surface-area reference for `get-shit-done/bin/gsd-tools.cjs` (Node CLI). For slash commands and user flows, see [Command Reference](COMMANDS.md).
+> Reference for the `gsd-tools` CLI (`get-shit-done/bin/gsd-tools.cjs`). For slash commands and user flows, see [Command Reference](COMMANDS.md). Return to [docs index](README.md).
 
 ---
 
@@ -493,7 +493,9 @@ API keys configured via `/gsd-settings` (`brave_search`, `firecrawl`, `exa_searc
 
 ---
 
-## See also
+## Related
 
-- [Architecture](ARCHITECTURE.md) — orchestration and runtime layering
-- [Command Reference](COMMANDS.md) — user-facing `/gsd-` commands
+- [Commands](COMMANDS.md)
+- [Configuration](CONFIGURATION.md)
+- [Architecture](ARCHITECTURE.md)
+- [docs index](README.md)