chore(catalog): rename coord to repo-mailbox, pin v0.3.0

The plugin repo moved from open/coord to open/repo-mailbox. Bumps the
entry name, source URL and ref together, and updates the README heading,
link and label to match.

Also corrects the per-plugin stat line: it claimed 48 selftest checks;
the actual count has been 70 since v0.2.2.

check-versions.mjs: 11 plugins, 10 OK, 1 WARN (pre-existing okr), 0 ERROR.

.claude-plugin/marketplace.json

@@ -101,11 +101,11 @@
       "description": "End-to-end facilitator for prompting Claude Design (claude.ai/design) — idea to copy-paste-ready prompt with iteration coaching, citing Anthropic primary sources."
     },
     {
-      "name": "coord",
+      "name": "repo-mailbox",
       "source": {
         "source": "url",
-        "url": "https://git.fromaitochitta.com/open/coord.git",
-        "ref": "v0.2.2"
+        "url": "https://git.fromaitochitta.com/open/repo-mailbox.git",
+        "ref": "v0.3.0"
       },
       "description": "Local mailbox for coordination between Claude Code sessions in different repositories — directed messages and broadcasts injected as context at session start. Local, private, no network."
     }

README.md

@@ -176,7 +176,7 @@ End-to-end facilitator for prompting Claude Design (`claude.ai/design`). Walks y
 
 ---
 
-### [Coord](https://git.fromaitochitta.com/open/coord) `v0.2.2`
+### [repo-mailbox](https://git.fromaitochitta.com/open/repo-mailbox) `v0.3.0`
 
 A local mailbox for coordination between Claude Code sessions in different repositories. Session A in repo X leaves a message for repo Y; the next session in repo Y gets it injected as context at startup. Local, private, no network, no SaaS.
 
@@ -184,7 +184,7 @@ A local mailbox for coordination between Claude Code sessions in different repos
 - **Untrusted by design** — message content is quote-prefixed and framed as untrusted data; send-side field sanitization blocks frontmatter injection
 - **Natural-language sending** — the `coord-send` skill maps "tell repo-x the bug is fixed" to the right delivery: broadcasts, bounded multi-target loops, replies, and deferred sends
 
-1 hook · 1 skill · 3 CLI scripts · 48 selftest checks · [Full documentation →](https://git.fromaitochitta.com/open/coord)
+1 hook · 1 skill · 3 CLI scripts · 70 selftest checks · [Full documentation →](https://git.fromaitochitta.com/open/repo-mailbox)
 
 ---