Drop "skills": ["./"] to fix v2.1.105 load regression

The harness rejects "./" in the skills array with
  Path escapes plugin directory: ./ (skills)
even though 2.1.94's changelog explicitly sanctioned this pattern.
This prevents the plugin from loading on current releases.

"./" also created a latent duplicate name: it registered the root
SKILL.md as "last30days", while auto-discovery of
skills/last30days-nux/SKILL.md (a symlink to ../../SKILL.md) registered
the same content under the same name. The duplicate only surfaced once
the registration succeeded.

Dropping "./" makes skills/ auto-discovery the single source for the
harness: skills/last30days-nux/ registers as "last30days", and
skills/last30days/ registers as "last30days-v3-spec" via its frontmatter
name. The root SKILL.md continues to serve the other harnesses that
rely on it (.agents/, .hermes-plugin/, .codex-plugin/, gemini-extension).

.claude-plugin/plugin.json

@@ -11,6 +11,5 @@
   "repository": "https://github.com/mvanhorn/last30days-skill",
   "license": "MIT",
   "keywords": ["research", "reddit", "twitter", "youtube", "tiktok", "instagram", "trends", "prompts", "polymarket", "github", "perplexity", "threads", "pinterest", "eli5", "hacker-news"],
-  "skills": ["./"],
   "hooks": {}
 }