Add missing manifest icons and PoC documentation

- Add emoji icon field to hello-dashboard, icd-test-runner,
  sdk-test-runner, and team-activity-log manifests
- Create README.md for tasks and schedules packages marking them
  as Proof of Concept with documented graduation criteria

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/team-activity-log/manifest.json

@@ -1,5 +1,6 @@
 {
   "id": "team-activity-log",
+  "icon": "📋",
   "title": "Team Activity Log",
   "type": "full",
   "tier": "starlark",