fix: restore /last30days slash command on Claude Code v2.1.105+ (#261)

Two regressions were silently breaking /last30days for every user:

1. plugin.json declared "skills": ["./"], which newer Claude Code
   rejects with "Path escapes plugin directory: ./ (skills)". The
   skill loader refused to register the command, so /last30days
   returned "Unknown command" even though /plugin list showed the
   plugin as installed. Fix: "skills": ["skills"] so the loader
   scans the real subdirectory.

2. marketplace.json pinned "version": "3.0.0" while plugin.json
   advertised "3.0.1". The /plugin resolver used the marketplace
   version and could install a phantom user-scope copy at a stale
   SHA alongside the correct project-scope install, creating
   duplicate skill-name collisions. Both manifests now agree on
   3.0.2.

Prior attempt: commit 93fbed2 fixed (1) before but got reverted.
This lands both fixes together in a tagged release so users can
/plugin update to recover.

Recovery for affected users is in CHANGELOG.md under 3.0.2.

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>

gemini-extension.json

@@ -1,6 +1,6 @@
 {
   "name": "last30days-skill",
-  "version": "3.0.1",
+  "version": "3.0.2",
   "description": "Research a topic from the last 30 days across Reddit, X, YouTube, TikTok, Instagram, Hacker News, Polymarket, and the web.",
   "settings": [
     {