feat(kyberforge): retarget agent-author to plugin-scope .apm/agents/

Plugin scope now authors a single vendor-neutral .apm/agents/<name>.agent.md
file (name/description/model/body only) instead of a Claude Code + Copilot
CLI pair, per ADR-0016: apm compile has no per-target field integrator, so
tools: and all Claude-only fields (isolation/maxTurns/effort/memory/
permissionMode) are omitted entirely rather than shipping a value that's
guaranteed wrong on one harness. Scope detection switches from a flat
plugin.json check to the same apm.yml+type: walk-up agent-audit's
validate.sh already uses. Project scope and user scope are unaffected —
both keep the existing dual-file pair model.

Refs: #89

plugins/kyberforge/skills/agent-author/scripts/README.md

@@ -2,12 +2,12 @@
 
 ## new-agent.sh
 
-Scaffolds agent definition files for both Claude Code and GitHub Copilot CLI from a single root directory input.
+Scaffolds agent definition file(s) from a single root directory input.
 
 ```
 Usage: new-agent.sh <agent-name> <root>
 ```
 
-Detects scope from the root: `plugin.json` present → plugin scope (both files in `<root>/agents/`); `~` → user scope (`~/.claude/agents/` + `~/.copilot/agents/`); otherwise project scope (`.claude/agents/` + `.github/agents/`). Each file is a no-op if it already exists. See `--help` for full usage.
+Resolves scope by walking up from `<root>`: a `type:`-bearing `apm.yml` found at or above `<root>` → plugin/APM scope (single file at `<package-root>/.apm/agents/<name>.agent.md`; an `apm.yml` without `type:` is a marketplace-only manifest and is skipped); `<root>` exactly `~` → user scope (`~/.claude/agents/` + `~/.copilot/agents/`); otherwise project scope (`<root>/.claude/agents/` + `<root>/.github/agents/`). Each file is a no-op if it already exists. See `--help` for full usage.
 
 Tests: `tests/new-agent.bats` (requires `bats-support` and `bats-assert`).