feat: consolidate marketplace skills into kyberforge plugin

Moves create-plugin, marketplace-architect, write-skill, and write-eval
from canonical .agents/skills/ into plugins/kyberforge/skills/, along
with all bundled sub-files, evals, and the plugin-marketplace-architecture
research doc. Bundles templates/plugin/ into create-plugin/assets/plugin-template/
so the skill is self-contained after install-time caching. Removes
templates/plugin/ and docs/research/plugin-marketplace-architecture.md
from the repo root as they are now exclusively in the plugin.

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

plugins/kyberforge/skills/create-plugin/assets/plugin-template/.claude-plugin/plugin.json

@@ -0,0 +1,8 @@
+{
+  "name": "PLUGIN_NAME",
+  "displayName": "PLUGIN_NAME",
+  "description": "PLUGIN_DESCRIPTION",
+  "author": { "name": "AUTHOR_NAME", "url": "AUTHOR_URL" },
+  "license": "MIT",
+  "keywords": []
+}