fix: resolve duplicate skill name causing marketplace validation failure (#204) (#214)

Two SKILL.md files declared `name: last30days` with `user-invocable: true`,
which caused strict marketplace validators to reject the plugin with "Some
plugins in this marketplace have validation errors":

- ./SKILL.md (canonical, also reachable via skills/last30days-nux/ symlink)
- ./skills/last30days/SKILL.md (v3 architecture spec, real file)

In v2.9.6, skills/last30days/SKILL.md was a symlink to ../../SKILL.md so
only one skill existed. Commit 0a9ff16 (v3.0.0) added a new real file at
skills/last30days-v3/SKILL.md, and commit 9be0780 then renamed that
directory to skills/last30days/, replacing the original symlink with a
different real file. The collision has been live since v3.0.0 shipped.

This change:
- Renames skills/last30days/SKILL.md to name: last30days-v3-spec and sets
  user-invocable: false. The file stays in place as internal architecture
  documentation, but it no longer competes with the canonical skill.
- Fixes README.md link that pointed to the deleted skills/last30days-v3/
  path (left over from the rename).
- Removes a stale variants/open/SKILL.md reference (variants/open was
  deleted in v3.0.0).

After the change, only one canonical name=last30days user-invocable=true
skill exists (the root SKILL.md, also reachable via the
skills/last30days-nux/ symlink, same inode).

Closes #204.

This contribution was developed with AI assistance (Codex).

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

skills/last30days/SKILL.md

@@ -1,14 +1,14 @@
 ---
-name: last30days
+name: last30days-v3-spec
 version: "3.0.0"
-description: "Multi-query social search with intelligent planning. Agent plans queries when possible, falls back to Gemini/OpenAI when not. Research any topic across Reddit, X, YouTube, TikTok, Instagram, Hacker News, Polymarket, and the web."
+description: "Internal architecture spec for the v3 last30days runtime pipeline. Not user-invocable."
 argument-hint: "last30days codex vs claude code"
 allowed-tools: Bash, Read, Write, WebSearch
 homepage: https://github.com/mvanhorn/last30days-skill
 repository: https://github.com/mvanhorn/last30days-skill
 author: mvanhorn
 license: MIT
-user-invocable: true
+user-invocable: false
 ---
 
 # last30days v3.0.0
@@ -86,7 +86,6 @@ fi
 - `yt-dlp` enables YouTube.
 - Planning and reranking fall back gracefully: Gemini -> OpenAI -> xAI -> deterministic/local.
 - Web retrieval stays within Brave/Serper dated results. Undated web hits are dropped.
-- For OpenClaw-specific watchlist, briefing, and history workflows, use `variants/open/SKILL.md`.
 
 ## Output model