Update README files to reflect the new Uklad Agent Toolkit package name

- Changed the installation command for the Uklad Agent Toolkit in the README files of core, devtools, and devtools-mcp to use the updated package name `ukladjs` instead of `uklad-agent-toolkit`.

These updates ensure consistency across documentation following the recent rebranding.

Author: flexsurfer

packages/core/README.md

@@ -16,7 +16,7 @@ Claude Code:
 
 ```text
 /plugin marketplace add ukladjs/agent-toolkit
-/plugin install uklad-agent-toolkit@uklad-agent-toolkit
+/plugin install uklad-agent-toolkit@ukladjs
 ```
 
 Codex:

packages/devtools-mcp/README.md

@@ -63,7 +63,7 @@ For Claude Code and Codex, don't configure this package by hand. The [Uklad Agen
 
 ```text
 /plugin marketplace add ukladjs/agent-toolkit
-/plugin install uklad-agent-toolkit@uklad-agent-toolkit
+/plugin install uklad-agent-toolkit@ukladjs
 ```
 
 **Codex**

packages/devtools/README.md

@@ -34,7 +34,7 @@ Install the [Uklad Agent Toolkit](https://github.com/ukladjs/agent-toolkit) plug
 
 ```text
 /plugin marketplace add ukladjs/agent-toolkit
-/plugin install uklad-agent-toolkit@uklad-agent-toolkit
+/plugin install uklad-agent-toolkit@ukladjs
 ```
 
 **Codex**