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/tests/README.md

@@ -0,0 +1,33 @@
+# tests/
+
+Test files for scripts bundled with this skill.
+
+## When to add tests
+
+Add tests here when the skill has scripts in `scripts/` that are complex enough
+to break silently — validators, parsers, generators, anything with branching
+logic or edge cases. Test infrastructure (`.bats`, `*_test.*`, `test_*.sh`)
+belongs here, not in `scripts/`.
+
+## Dependencies
+
+Tests require [bats-support](https://github.com/bats-core/bats-support) and
+[bats-assert](https://github.com/bats-core/bats-assert). The test files load
+helpers from the repo root's `tests/test_helper/`.
+
+From the repo root:
+
+```bash
+git clone https://github.com/bats-core/bats-support tests/test_helper/bats-support
+git clone https://github.com/bats-core/bats-assert tests/test_helper/bats-assert
+```
+
+Run all tests for this skill (from the repo root):
+
+```bash
+bats plugins/kyberforge/skills/agent-author/tests/
+```
+
+## If no tests are needed
+
+Delete this README and the `tests/` directory entirely.