docs(i18n): address ds-review-bot round-2 — switcher placeholders, regex anchor, contract completeness

新增 {{source_filename}}/{{source_filename_zh}} 占位符：切换行指令
可执行化，新配对（源文件尚无切换行）也必须生成（critical）。加粗
后空格规则限定于拉丁字母/数字，不再与全角标点规则冲突。日期匹配
锚定 basename 开头，release-notes-2026-* 类文件不再误判。金标
development.zh 补回 RFC 指引句与 agent 首现括注、pre-push 描述改
为 check:pre-push 调度器实况。术语表补回单文件可执行 RFC 配对在用
的 5 行（VFS/deploy root/peer dependency/serving surface/wheel）。
双语 README 的门禁清单补第 4 条（日期分界强制配对）。

scripts/verify-translation-pairing.ts

@@ -257,7 +257,7 @@ for (const req of manifest.required) {
 // 2. Date-named documents (RFCs) dated on/after the requiredSince cutoff merge
 // bilingual: a new RFC lands with its pair or not at all. Deterministic from
 // the filename alone — no git history, so it holds on shallow CI checkouts.
-const DATED = /(\d{4}-\d{2}-\d{2})-[^/]*\.md$/
+const DATED = /(?:^|\/)(\d{4}-\d{2}-\d{2})-[^/]*\.md$/
 for (const source of sources) {
   if (isExcluded(source)) continue
   const dated = DATED.exec(source)