docs(skill): rename marketplace openkb-marketplace → vectify

The previous name caused a stutter at the install site:
`/plugin install openkb@openkb-marketplace`. The marketplace
identifier should describe the publisher, not duplicate the
product name. Mirrors Anthropic's pattern
(`anthropic-agent-skills`) but in the shorter form appropriate
for a single-publisher catalog.

Install now reads cleanly: `/plugin install openkb@vectify`.

Aside: `.claude-plugin/plugin.json` (used by mattpocock/skills) is
NOT a Claude Code marketplace manifest — it's a custom schema for
the vercel-labs/skills `npx` tool. `/plugin marketplace add` requires
`marketplace.json` specifically, which we already have. So no need
to mirror mattpocock's minimal plugin.json.

Author: KylinMountain

.claude-plugin/marketplace.json

@@ -1,5 +1,5 @@
 {
-  "name": "openkb-marketplace",
+  "name": "vectify",
   "owner": {
     "name": "VectifyAI",
     "email": "team@vectify.ai"

README.md

@@ -244,7 +244,7 @@ OpenKB ships a [SKILL.md](https://agentskills.io/) so any agent CLI can read you
 
 ```
 /plugin marketplace add VectifyAI/OpenKB
-/plugin install openkb@openkb-marketplace
+/plugin install openkb@vectify
 ```
 
 **Gemini CLI** (native skills installer):