feat(plugin): publish as Claude Code marketplace plugin

Update .claude-plugin/marketplace.json and plugin.json to v2.9.5 with
full metadata. Add plugin install instructions to README as the
recommended install method. The repo root serves as both the marketplace
and the plugin - skills/last30days/SKILL.md (symlink) is discovered
automatically.

Users can now install with:
  /plugin marketplace add mvanhorn/last30days-skill
  /plugin install last30days@last30days-skill

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude-plugin/plugin.json

@@ -1,12 +1,25 @@
 {
   "name": "last30days",
-  "description": "Research any topic from the last 30 days across Reddit, X, YouTube, and the web",
-  "version": "2.9.1",
+  "version": "2.9.5",
+  "description": "Research any topic from the last 30 days across Reddit, X, YouTube, TikTok, Instagram, Hacker News, Polymarket, and the web.",
   "author": {
-    "name": "mvanhorn"
+    "name": "Matt Van Horn",
+    "email": "mvanhorn@gmail.com",
+    "url": "https://github.com/mvanhorn"
   },
+  "homepage": "https://github.com/mvanhorn/last30days-skill",
   "repository": "https://github.com/mvanhorn/last30days-skill",
   "license": "MIT",
-  "keywords": ["research", "reddit", "twitter", "x", "youtube", "trends", "prompts"],
+  "keywords": [
+    "research",
+    "reddit",
+    "twitter",
+    "youtube",
+    "tiktok",
+    "instagram",
+    "trends",
+    "prompts",
+    "polymarket"
+  ],
   "skills": ["./"]
 }