feat: add signals-dashboard canvas extension

The dashboard is the centerpiece — real-time agent coordination
view showing desk status, signal types, intent text, outcome
pairing with honesty gap, token usage, and stash/restore controls.

Includes all updates from the-workshop PRs #3-#7:
- Empty state guidance for new users
- Token usage display per desk
- TA partnership signals + Cairn awareness
- Intent-as-text (execution signals use descriptive text)
- Outcome signal pairing with honesty gap calibration
- Open desk button
- Subtype labels (done/checkpoint/blocked/hands-up)

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

extensions/signals-dashboard/.github/plugin/plugin.json

@@ -0,0 +1,17 @@
+{
+  "name": "signals-dashboard",
+  "description": "Real-time agent coordination dashboard for The Workshop. Shows desk status, signal types (done, checkpoint, blocked, hands-up, partnership), intent text, outcome pairing with honesty gap, token usage, and stash/restore controls.",
+  "version": "0.1.0",
+  "author": {
+    "name": "jennyf19",
+    "url": "https://github.com/jennyf19"
+  },
+  "keywords": [
+    "agent-signals",
+    "dashboard",
+    "multi-agent",
+    "coordination",
+    "canvas"
+  ],
+  "extensions": "."
+}