fix: remove duplicate /last30days command wrapper (#461) (#462)

* fix: remove duplicate command wrapper so plugin exposes only the skill (#461)

The plugin shipped both commands/last30days.md and the skill under the
same name, so /last30 surfaced two `last30days` entries with two
different descriptions. Remove the wrapper; the skill already carries
its own argument-hint, so the /last30days <topic> picker UX is unchanged.

Also corrects the README install note that claimed Claude Code dedupes
the slash command across install methods (it does not), and bumps
3.3.0 -> 3.3.1 across plugin.json, marketplace.json, gemini-extension.json,
and SKILL.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix: bump pyproject.toml version to 3.3.1 (manifest contract)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore: update uv.lock for 3.3.1 version bump

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gemini-extension.json

@@ -1,6 +1,6 @@
 {
   "name": "last30days-skill",
-  "version": "3.3.0",
+  "version": "3.3.1",
   "description": "Research a topic from the last 30 days across Reddit, X, YouTube, TikTok, Instagram, Hacker News, Polymarket, and the web.",
   "settings": [
     {