docs(rfc): restore the checkpoint paragraph break lost in the loopx-project#4894 merge

The loopx-project#4894 merge resolved an additive conflict in
`typescript-control-plane-migration-v0.md` by keeping both checkpoint
paragraphs, but the blank line between them was staged only in the zh-CN
mirror, so the English section renders the two entries as one paragraph
while the mirror renders two. Restore the missing paragraph break; no text
is added, removed or reordered.

Signed-off-by: huangruiteng <14976749+huangruiteng@users.noreply.github.com>

Author: huangruiteng

docs/architecture/rfcs/typescript-control-plane-migration-v0.md

@@ -33,6 +33,7 @@ This closes a concurrency/current-proof slice of L2/L3, not whole-Goal migration
 default onboarding, contributor-owned SQLite D2 or T4 Python retirement. The
 [operator contract](../../reference/canonical-lease-renew.md#commit-retry-and-readback)
 distinguishes historical results from present execution.
+
 Handoff-mode transition now shares typed ownership facts and an explicit
 valid/invalid previous-mode state across legacy and canonical paths. Python's
 blocker classification, artificial previous mode and whole-text rewrite are