feat(kyberforge): add agent-author skill for Claude Code and Copilot CLI agents

## Why

skill-author explicitly excludes agent definition files ("Do not use to author
agent definition files"). No factory skill existed to create or improve the
.md / .agent.md files that define Claude Code subagents and Copilot CLI agents
in a plugin, project, or user scope. This fills that gap.

## Implementation Notes

Single-root scaffold convention: new-agent.sh <name> <root> derives both
provider file paths from the root by convention — plugin scope (plugin.json
present) writes both files into <root>/agents/; non-plugin scope writes
.claude/agents/<name>.md and .github/agents/<name>.agent.md. This keeps
input minimal while always generating both provider files. See ADR-0015.

Routing is file-level (not directory-level like skill-author): neither file
exists → create flow; at least one exists → improve flow; scaffold is a
file-by-file no-op so retries are safe.

No companion agent-audit skill — inline validation in the close step covers
the simpler agent field contract. agent-audit is tracked as a follow-on.

## Impact

Closes the skill-author gap for agent definitions. Follow-ons tracked in
Gitea #11: agent-audit skill and --copilot-dest override flag for non-standard
Copilot project paths.

---
ADR: docs/adr/0015-agent-author-dual-provider-scaffold.md
Refs: #10
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/kyberforge/skills/agent-author/references/sources.md

@@ -0,0 +1,68 @@
+---
+source_keys:
+  - context7-websites-code-claude
+  - claude-code-plugins-docs
+  - claude-code-subagents-docs
+  - context7-github-en-copilot
+  - github-custom-agents-configuration
+  - github-cli-plugin-reference
+  - github-plugins-creating
+---
+
+# Sources
+
+## context7-websites-code-claude
+
+- **URL:** context7:/websites/code_claude
+- **Research doc:** plugins/kyberforge/docs/research/docs/claude-code-plugins/sources.md
+- **Description:** Official Claude Code documentation site indexed by Context7 — plugin manifest schema, subagent definition types, marketplace JSON format, agent markdown file format
+- **Contributing files:** SKILL.md, assets/templates/claude-code.md, references/deployment-modes.md
+- **Status:** `extracted`
+
+## claude-code-plugins-docs
+
+- **URL:** https://code.claude.com/docs/en/plugins
+- **Research doc:** plugins/kyberforge/docs/research/docs/claude-code-plugins/sources.md
+- **Description:** Official Claude Code plugin authoring guide — plugin structure, manifest fields, loading methods, skill namespacing, agent activation, marketplace submission
+- **Contributing files:** SKILL.md, references/deployment-modes.md
+- **Status:** `extracted`
+
+## claude-code-subagents-docs
+
+- **URL:** https://code.claude.com/docs/en/sub-agents
+- **Research doc:** plugins/kyberforge/docs/research/docs/claude-code-plugins/sources.md
+- **Description:** Official Claude Code subagent reference — definition format, all frontmatter fields, scope priority, built-in agents, CLI flags, environment variables, known limitations
+- **Contributing files:** SKILL.md, assets/templates/claude-code.md, references/deployment-modes.md
+- **Status:** `extracted`
+
+## context7-github-en-copilot
+
+- **URL:** context7:/websites/github_en_copilot
+- **Research doc:** plugins/kyberforge/docs/research/docs/github-copilot-plugins/sources.md
+- **Description:** Official GitHub Copilot documentation indexed by Context7; covers CLI plugins, custom agents, SDK, and marketplace
+- **Contributing files:** SKILL.md, assets/templates/copilot.agent.md, references/deployment-modes.md
+- **Status:** `extracted`
+
+## github-custom-agents-configuration
+
+- **URL:** https://docs.github.com/en/copilot/reference/custom-agents-configuration
+- **Research doc:** plugins/kyberforge/docs/research/docs/github-copilot-plugins/sources.md
+- **Description:** Reference for cloud and IDE custom agent definition format — frontmatter fields, tool aliases, MCP server config, secrets interpolation, scoping hierarchy
+- **Contributing files:** SKILL.md, assets/templates/copilot.agent.md, references/deployment-modes.md
+- **Status:** `extracted`
+
+## github-cli-plugin-reference
+
+- **URL:** https://docs.github.com/en/copilot/reference/copilot-cli-reference/cli-plugin-reference
+- **Research doc:** plugins/kyberforge/docs/research/docs/github-copilot-plugins/sources.md
+- **Description:** Full CLI plugin reference — plugin.json schema, marketplace.json schema, all CLI commands and flags, install specification formats, loading precedence, env vars, LSP config
+- **Contributing files:** SKILL.md, scripts/new-agent.sh, references/deployment-modes.md
+- **Status:** `extracted`
+
+## github-plugins-creating
+
+- **URL:** https://docs.github.com/en/copilot/how-tos/copilot-cli/customize-copilot/plugins-creating
+- **Research doc:** plugins/kyberforge/docs/research/docs/github-copilot-plugins/sources.md
+- **Description:** How-to for creating Copilot CLI plugins — plugin structure, agent and skill authoring, hooks format, MCP config, development lifecycle
+- **Contributing files:** SKILL.md, assets/templates/copilot.agent.md
+- **Status:** `extracted`