Add plugin builder for one-file client install

plugin/make-plugin.{sh,ps1} stamp a user's own Freshservice API key and the
shared server token into a template and emit a personalized freshservice.plugin
(direct HTTP MCP connection — no Node/mcp-remote/config editing on clients).
Built plugins embed credentials, so *.plugin is git-ignored; the committed
template holds only placeholders. Validated with 'claude plugin validate'.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugin/template/README.md

@@ -0,0 +1,20 @@
+# Freshservice plugin
+
+Connects Claude (Desktop / Cowork) to the PESCO Freshservice service desk
+through the shared MCP server on the LAN. Tickets, assets/CMDB, people, and
+change/problem/release records — with every action attributed to **your own**
+Freshservice agent account.
+
+## This file is personalized
+
+This plugin was generated by `make-plugin` and contains **your** Freshservice
+API key and the shared server token. Treat it like a password:
+
+- Do **not** share your `.plugin` file with anyone else — they would act as you.
+- If your key is exposed, regenerate it in Freshservice (Profile settings →
+  API key) and rebuild the plugin.
+
+## Requirements
+
+- You must be an agent in the PESCO Freshservice instance.
+- Your computer must be able to reach the LAN server (on-site network or VPN).