feat: add kyberforge plugin and rename plugin-create skill

Scaffolds the kyberforge marketplace management plugin (create-plugin and
marketplace-architect skills will live here). Renames the plugin-create
skill directory to create-plugin to match the canonical kebab-order convention.

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

plugins/kyberforge/agents/README.md

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+# agents/
+
+Agent definitions for this plugin. Each agent needs two files — one per tool:
+
+| File | Tool | Notes |
+|---|---|---|
+| `<name>.md` | Claude Code | Frontmatter: `name`, `description`. No `tools:` field. |
+| `<name>.agent.md` | GitHub Copilot CLI | Frontmatter: `name`, `description`, `tools:` (array of permitted tool names). |
+
+The two files share the same system prompt body. Keep them in sync.
+
+Rename `PLUGIN_NAME.md` and `PLUGIN_NAME.agent.md` to your agent's name (kebab-case).
+Add additional agent pairs as needed — one pair per agent.

plugins/kyberforge/agents/kyberforge.agent.md

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+---
+name: kyberforge
+description: Skills and agents for creating, maintaining, and managing a Claude Code / Copilot CLI plugin marketplace.
+tools:
+  - read_file
+  - list_directory
+---
+
+Replace this with your agent's system prompt and instructions.
+
+This file is loaded by **GitHub Copilot CLI**. The `tools:` frontmatter field declares
+which tools the agent can use — add or remove tools as needed.
+For Claude Code, see `kyberforge.md`.

plugins/kyberforge/agents/kyberforge.md

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+---
+name: kyberforge
+description: Skills and agents for creating, maintaining, and managing a Claude Code / Copilot CLI plugin marketplace.
+---
+
+Replace this with your agent's system prompt and instructions.
+
+This file is loaded by **Claude Code**. For GitHub Copilot CLI, see `kyberforge.agent.md`.