feat(commands): add /essay-edit command for expert essay editing

Pairs with /essay-outline. Runs structural review via story-lens skill
(Saunders framework), then granular line-level editing. Guards against
timid scribe syndrome and preserves author voice via john-voice skill.
Outputs a fully edited essay to docs/essays/.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -11,8 +11,8 @@
   "plugins": [
     {
       "name": "compound-engineering",
-      "description": "AI-powered development tools that get smarter with every use. Make each unit of engineering work easier than the last. Includes 25 specialized agents, 24 commands, and 24 skills.",
-      "version": "2.38.0",
+      "description": "AI-powered development tools that get smarter with every use. Make each unit of engineering work easier than the last. Includes 25 specialized agents, 25 commands, and 24 skills.",
+      "version": "2.39.0",
       "author": {
         "name": "Kieran Klaassen",
         "url": "https://github.com/kieranklaassen",