chore: add SECURITY.md and broken API issue template

- SECURITY.md documents endpoint stability per area, how to report
  broken Graph endpoints, and links to the MS Graph changelog
- New issue template for broken API reports with structured fields
  (page, error, date, endpoint, license tier)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/broken_api.md

@@ -0,0 +1,28 @@
+---
+name: Broken API Endpoint
+about: A dashboard card stopped working due to a Microsoft Graph API change
+title: '[BROKEN API] '
+labels: broken-api
+assignees: ''
+---
+
+**Which page and card is affected?**
+e.g. Identity page → Risk Detections card
+
+**What error is shown on screen?**
+e.g. 403 Forbidden / 404 Not Found / blank card
+
+**When did it stop working?**
+Approximate date:
+
+**Graph endpoint involved (if known):**
+e.g. `/v1.0/identityProtection/riskDetections`
+
+**Link to Microsoft changelog (if you found it):**
+https://developer.microsoft.com/en-us/graph/changelog
+
+**Your tenant license (helps narrow down the issue):**
+- [ ] Microsoft 365 Business Premium
+- [ ] Microsoft 365 E3
+- [ ] Microsoft 365 E5
+- [ ] Other: