docs(i18n): core-data-structures and postmortem batch — 22 bilingual pairs

core-data-structures 18 篇（core.md 因超长仍在产出、随后补）、
postmortem 3 篇与 RFC 前门 README 配对；流水线 + 二遍校验产出。
生成文件 docs/rfc/INDEX.md（gen-rfc-index 产物）列入排除。中文侧
页内锚点统一指向英文侧锚名，满足配对门禁的链接目标一致规则。

docs/core-data-structures/session.md

@@ -1,5 +1,7 @@
 # Sessions
 
+English | [中文](session.zh.md)
+
 The in-memory, event-sourced model of [dsh-session](../../packages/core/session). A `Session` is an **append-only log** of typed `SessionEvent`s — the single source of truth for an agent's whole interaction history. The LLM message history is *derived* from the log, never stored separately; replay is re-derivation from the same events. How the log is made **durable** (the persistence seam, backends, crash recovery) is the sibling concern on [persistence.md](persistence.md).
 
 Source: [`packages/core/session/src/types.ts`](../../packages/core/session/src/types.ts)