docs: add Copilot CLI hook setup to notifications guide (#1875)

* docs: add Copilot CLI hook setup to notifications guide

Add GitHub Copilot CLI section with hooks for notifications and
sidebar status pills (userPromptSubmitted, agentStop, errorOccurred,
sessionEnd). Includes link to official GitHub hooks documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* docs: address PR feedback for Copilot CLI hooks

- Use if/else instead of &&/|| to avoid false-positive osascript fallback
- Fix jq path: .error.message → .errorMessage for Copilot CLI schema
- Remove --icon/--color flags (let cmux handle styling)
- Add clear-notifications side-effect note
- Add concrete repo-level config example
- Document set-status/clear-status in CLI Commands section

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Harley Adams <harley.adams@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docs/notifications.md

@@ -58,6 +58,57 @@ cmux notify --title "Done" --tab 0 --panel 1
 
 See the [Claude Code documentation](https://docs.anthropic.com/en/docs/claude-code) for hook configuration.
 
+### GitHub Copilot CLI
+
+Copilot CLI supports [hooks](https://docs.github.com/en/copilot/how-tos/use-copilot-agents/coding-agent/use-hooks) that run shell commands at key lifecycle events. Add to `~/.copilot/config.json`:
+
+```json
+{
+  "hooks": {
+    "userPromptSubmitted": [
+      {
+        "type": "command",
+        "bash": "if command -v cmux &>/dev/null; then cmux set-status copilot_cli Running; fi",
+        "timeoutSec": 3
+      }
+    ],
+    "agentStop": [
+      {
+        "type": "command",
+        "bash": "if command -v cmux &>/dev/null; then cmux notify --title 'Copilot CLI' --body 'Done'; cmux set-status copilot_cli Idle; else osascript -e 'display notification \"Done\" with title \"Copilot CLI\"'; fi",
+        "timeoutSec": 5
+      }
+    ],
+    "errorOccurred": [
+      {
+        "type": "command",
+        "bash": "if command -v cmux &>/dev/null; then cmux notify --title 'Copilot CLI' --subtitle 'Error' --body \"$(cat | jq -r '.errorMessage // \"An error occurred\"' 2>/dev/null | head -c 100)\"; cmux set-status copilot_cli Error; else osascript -e 'display notification \"An error occurred\" with title \"Copilot CLI\"'; fi",
+        "timeoutSec": 5
+      }
+    ],
+    "sessionEnd": [
+      {
+        "type": "command",
+        "bash": "if command -v cmux &>/dev/null; then cmux clear-status copilot_cli; fi",
+        "timeoutSec": 3
+      }
+    ]
+  }
+}
+```
+
+Or for repo-level hooks, create `.github/hooks/notify.json`:
+
+```json
+{
+  "version": 1,
+  "hooks": {
+    "userPromptSubmitted": [ ... ],
+    "agentStop": [ ... ]
+  }
+}
+```
+
 ### OpenAI Codex
 
 Add to `~/.codex/config.toml`:
@@ -119,6 +170,8 @@ cmux sets these in child shells:
 cmux notify --title <text> [--subtitle <text>] [--body <text>] [--tab <id|index>] [--panel <id|index>]
 cmux list-notifications
 cmux clear-notifications
+cmux set-status <key> <value>
+cmux clear-status <key>
 cmux ping
 ```