feat(i18n): new documents merge bilingual — the requiredSince date frontier

New docs must not enlarge the translation backlog: any date-named
document (yyyy-mm-dd-*.md, i.e. an RFC) dated on/after the manifest's
requiredSince cutoff must merge with its complete pair, independent of
the required back-catalog list. Cutoff ships at 2026-07-05, so the
existing 2026-07-04 RFC wave is grandfathered into the batch backlog
and everything after is bilingual from birth.

The date comes from the filename, deliberately: it is deterministic
from tree content alone — no git history (shallow CI checkouts hold),
no PR base ref — matching the gate's pure-content design. A proposal
dated before the cutoff that merges later escapes the rule; that is
the graceful grandfathering of in-flight work, not a hole.

--list marks such files (required by date); contract and RFC updated
in both languages and the pairs re-recorded.

docs/i18n/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-README.md: 6e2bbd27c3288037bafeb6cc71b801d56b956ab4
-README.zh.md: 04c99ae336cf1e96cbc185f0ccbd063ef8977944
+README.md: ba3431c72d9f2a86220df4ed682620514401291f
+README.zh.md: 02957c97937525a1da27242620a8327b863de040

docs/i18n/README.md

@@ -43,7 +43,7 @@ The gate's limit, stated plainly: **a green gate means the pair was confirmed co
 - `docs/AGENTS.md` — agent instructions, maintained in English only like the root `AGENTS.md`.
 - `docs/i18n/terminology.md` — the terminology table is itself bilingual by construction.
 
-**Rollout**: the `required` list in the manifest is the enforcement frontier, not the goal. The goal is full bilingual coverage of the scope. Pairs land in reviewable batches (core entry docs, cookbook, RFCs, postmortems, …); each merged batch adds its files to `required`, so the gate ratchets forward and never regresses. Documents not yet in `required` are backlog — visible in `--list` — but any pair that already exists is held to the full contract regardless of the list. Pairing a document is a commitment: every later edit to either side must carry the counterpart along, so grow the frontier at the pace translation review is actually resourced, not ahead of it.
+**Rollout**: new documents don't wait for a batch — a date-named document (`yyyy-mm-dd-*.md`, i.e. an RFC) dated on or after the manifest's `requiredSince` cutoff must merge with its pair, so everything new is bilingual from birth. For the back-catalog, the `required` list in the manifest is the enforcement frontier, not the goal. The goal is full bilingual coverage of the scope. Pairs land in reviewable batches (core entry docs, cookbook, RFCs, postmortems, …); each merged batch adds its files to `required`, so the gate ratchets forward and never regresses. Documents not yet in `required` are backlog — visible in `--list` — but any pair that already exists is held to the full contract regardless of the list. Pairing a document is a commitment: every later edit to either side must carry the counterpart along, so grow the frontier at the pace translation review is actually resourced, not ahead of it.
 
 ## Division of labor
 

docs/i18n/README.zh.md

@@ -43,7 +43,7 @@
 - `docs/AGENTS.md`——agent 指令，与根 `AGENTS.md` 一样只以英文维护。
 - `docs/i18n/terminology.md`——术语表本身即是双语构造。
 
-**推进**：manifest 中的 `required` 列表是强制边界，不是目标。目标是范围内的全量双语覆盖。配对按可评审的批次落地（核心入口文档、cookbook、RFC、postmortem……）；每个批次合入后把其文件加进 `required`，门禁只进不退。尚未进入 `required` 的文档是 backlog——在 `--list` 中可见——但任何已存在的配对无论在不在清单里都按完整契约检查。给一篇文档配对是一份承诺：此后对任一侧的每次修改都必须带上另一侧，所以边界的扩张要跟上翻译评审的实际投入节奏，不要抢在前面。
+**推进**：新文档不等批次——文件名带日期的文档（`yyyy-mm-dd-*.md`，即 RFC）日期在 manifest 的 `requiredSince` 当天或之后，就必须连同配对一起合入，新增的一切生来即是双语。对于存量文档，manifest 中的 `required` 列表是强制边界，不是目标。目标是范围内的全量双语覆盖。配对按可评审的批次落地（核心入口文档、cookbook、RFC、postmortem……）；每个批次合入后把其文件加进 `required`，门禁只进不退。尚未进入 `required` 的文档是 backlog——在 `--list` 中可见——但任何已存在的配对无论在不在清单里都按完整契约检查。给一篇文档配对是一份承诺：此后对任一侧的每次修改都必须带上另一侧，所以边界的扩张要跟上翻译评审的实际投入节奏，不要抢在前面。
 
 ## 分工