chore(catalog): correct repo-mailbox stat line (1006 -> 1187 selftest checks)

Catalog stat line was stale against repo-mailbox main (deb3707, 0.37.0):
badge reads selftest_checks-1187, catalog said 1006. Hooks/skills/CLI
scripts already matched (1/4/8) so only the selftest count changes.
This unblocks scripts/release-plugin.mjs repo-mailbox --create-tag,
whose pre-flight compares the catalog line against the target
version's README (tag missing, falls back to worktree = 1187).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -220,7 +220,7 @@ A local mailbox for coordination between Claude Code sessions in different repos
 - **`route`** — turns four scored traits of the next task into a model/effort row from a closed six-row rubric, with a pasteable startup command and a one-row-cheaper fallback
 - **`dispatch`** — hands work to a session in another repo as a complete, verified startup command: the prompt written to a file, model and effort derived from the rubric, output form chosen by whether the target repo already has a terminal pane
 
-1 hook · 4 skills · 8 CLI scripts · 1006 selftest checks · [Full documentation →](https://git.fromaitochitta.com/open/repo-mailbox)
+1 hook · 4 skills · 8 CLI scripts · 1187 selftest checks · [Full documentation →](https://git.fromaitochitta.com/open/repo-mailbox)
 
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