chore(release): 0.12.1 -- coord-send stops silently falling back to a stale copy

Version sync across plugin.json, package.json, README badge, CHANGELOG and
all three skill frontmatters, plus the 156 -> 159 selftest-count references
that follow from the previous commit's three new checks.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YJMJanRHkUhEf9EYxMpbM5

CHANGELOG.md

@@ -5,6 +5,21 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.12.1] - 2026-07-31
+
+### Fixed
+
+- **`coord-send`'s own script-path expression fell back to a stale deployed
+  copy.** A Bash tool call never has `CLAUDE_PLUGIN_ROOT` set as a real shell
+  variable — only the skill's own markdown rendering resolves that bare
+  token — so the `${CLAUDE_PLUGIN_ROOT:-$HOME/.claude}` fallback silently won
+  every time the engine line was actually executed, routing through whatever
+  the operator's personal `~/.claude/scripts/coord-send.sh` happened to be
+  instead of the plugin's own bundled script. Same defect class `board.sh`
+  was already fixed for. Reported live by org-ops: a `--fyi` send hit an old
+  deployed copy lacking the flag. `coord-selftest.sh` grows three checks
+  (156 -> 159) pinning the fix.
+
 ## [0.12.0] - 2026-07-31
 
 ### Fixed