fix(kyberforge): clarify skill descriptions, trim gotchas, and clean up marketplace-author

## Why
Several small quality issues accumulated across plugin-author and
marketplace-author: the plugin-author description was ambiguous about
scope, the ADD flow asked an unnecessary clarifying question when local
path is the obvious default, VALIDATE had redundant wording already
captured inline, the keywords field was missing from the validation
checklist, and tests/README.md was a placeholder with nothing to test.

## Implementation Notes
- plugin-author: tightened description scope to "inside those
  directories"; added `keywords` identical-in-both-manifests check to
  VALIDATE checklist.
- marketplace-author: moved reserved-prefix constraint from gotchas
  into the ADD checklist item; replaced the four-option prompt with a
  default+escape-hatch ("I'll treat this as local path — is that right?");
  folded the validate-from-root note inline and removed trailing padding;
  deleted tests/README.md — no scripts/ directory exists, so the
  placeholder was noise.
- README.md: removed the tests/README.md row from the file table.

plugins/kyberforge/skills/plugin-author/SKILL.md

@@ -7,8 +7,8 @@ description: >
   ("release", "tag", "publish"). Manages both Claude Code
   (.claude-plugin/plugin.json) and Copilot CLI (plugin.json) manifests in one
   pass. Do not use when the request is about plugin content (skills, agents,
-  hooks, MCP servers) or marketplace.json entries — use /marketplace-author
-  for those.
+  hooks, or MCP servers inside those directories). Do not use for
+  marketplace.json entries — use /marketplace-author for that.
 allowed-tools: Bash Read Write Edit
 metadata:
   category: factory
@@ -104,6 +104,7 @@ Check:
 - [ ] `version` identical in both manifests (version parity — ADR-0016)
 - [ ] `author.name` identical in both manifests
 - [ ] `license` identical in both manifests
+- [ ] `keywords` identical in both manifests
 - [ ] No `FILL_IN_*` placeholders remain
 - [ ] `displayName` present in CC manifest only
 - [ ] `author.url` in CC manifest, `author.email` in Copilot manifest