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/write-skill/META.md

@@ -0,0 +1,16 @@
+```yaml
+version: "1.5"
+updated: 2026-05-26
+
+# when: describes when this skill is loaded — the full trigger context.
+# More detail than the description field; not used for routing.
+when: invoked by explicit trigger ("write a new skill for X", "create a SKILL.md that does Y") or implicit request to author a skill file or convert an existing placeholder to the canonical authoring standard
+
+# source: omitted — self-authored original; no upstream content adopted
+# Absence of source means self-authored. If content is adopted from upstream,
+# add a source entry per the META-TEMPLATE.md schema.
+
+references:
+  - https://agentskills.io/specification.md
+  - https://agentskills.io/skill-creation/optimizing-descriptions
+```