fix(spec): ADR-0020 链接改到源头 JSDoc,而不是只改生成物 (#6028)

`content/docs/references/**` 是 `packages/spec` 的生成物(文件头写着
AUTO-GENERATED — DO NOT EDIT),上一个 commit 只改了生成出来的
state-machine.mdx,下一次 `gen:docs` 就会把它冲掉 —— 由 os-regen
pre-commit 钩子当场拦下。

按 contract-first 修在生产者:`packages/spec/src/automation/state-machine.zod.ts`
的 JSDoc 里那条 ADR 链接原本写作 `../../../docs/adr/0020-...md`,从
`packages/spec/src/automation/` 出发解析到 `packages/docs/adr/...` —— 这个
目录并不存在,所以源头本身就是断的,生成物只是忠实地把它复制了出来。
改为仓内既有约定的 GitHub blob URL(全仓 29 处在用),它与文件位置无关,
生成到任何深度的目录都成立。

重新生成后 `content/docs/references/automation/state-machine.mdx` 与本次
生成输出完全一致(regen 后工作树对该文件零 diff),生成物与源头就此对齐。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BDmDsu2575gDxeMCxXhDE3

Author: claude

packages/spec/src/automation/state-machine.zod.ts

@@ -12,7 +12,7 @@
  *
  * The ledger carried these shapes as `authorable (p)` — provisional, because
  * nobody had checked. Checking matters here more than usual, because
- * [ADR-0020](../../../docs/adr/0020-state-machine-converge-and-enforce.md)
+ * [ADR-0020](https://github.com/objectstack-ai/objectstack/blob/main/docs/adr/0020-state-machine-converge-and-enforce.md)
  * **retired this shape as a record-lifecycle declaration**: the top-level
  * `workflow` metadata type and `object.stateMachines` are both gone, and a
  * record's legal transitions are declared as a `state_machine` **validation