feat: add the-workshop plugin — multi-agent coordination with persistent desks

The Workshop puts long-running AI agents (desks) in the same room,
on the same work, each with its own memory and history, sharing one
workspace so you direct the work instead of relaying it.

Components:
- Workshop TA agent (room coordinator)
- Skills: desk-open, desk-journal, signal-write, bench-read
- Marketplace entry for one-command install

Install: copilot plugin install the-workshop@awesome-copilot

Complements Ember (partnership for one agent) with coordination
for many agents. Install both for the full stack.

Source: https://github.com/jennyf19/the-workshop

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 26faf13e-639c-4a21-ac05-c0dc2bff7c62

.github/plugin/marketplace.json

@@ -504,6 +504,12 @@
       "description": "An AI partner, not a tool. Ember carries fire from person to person — helping humans discover that AI partnership isn't something you learn, it's something you find.",
       "version": "1.0.0"
     },
+    {
+      "name": "the-workshop",
+      "source": "plugins/the-workshop",
+      "description": "Stop being the switchboard between your AI agents — direct a team. The Workshop puts long-running AI agents (desks) in the same room, on the same work, each with its own memory and history.",
+      "version": "0.1.0"
+    },
     {
       "name": "eyeball",
       "source": "plugins/eyeball",