Add channel test providers for Email, Slack, Teams, and Webhook

- Implemented EmailChannelTestProvider to generate email preview payloads.
- Implemented SlackChannelTestProvider to create Slack message previews.
- Implemented TeamsChannelTestProvider for generating Teams Adaptive Card previews.
- Implemented WebhookChannelTestProvider to create webhook payloads.
- Added INotifyChannelTestProvider interface for channel-specific preview generation.
- Created ChannelTestPreviewContracts for request and response models.
- Developed NotifyChannelTestService to handle test send requests and generate previews.
- Added rate limit policies for test sends and delivery history.
- Implemented unit tests for service registration and binding.
- Updated project files to include necessary dependencies and configurations.

docs/README.md

@@ -72,16 +72,17 @@ Everything here is open‑source and versioned — when you check out a git ta
 - **21 – [Install Guide](21_INSTALL_GUIDE.md)**
 - **22 – [CI/CD Recipes Library](ci/20_CI_RECIPES.md)**
 - **23 – [FAQ](23_FAQ_MATRIX.md)**
-- **24 – [Offline Update Kit Admin Guide](24_OFFLINE_KIT.md)**
-- **25 – [Concelier Apple Connector Operations](ops/concelier-apple-operations.md)**
-- **26 – [Authority Key Rotation Playbook](ops/authority-key-rotation.md)**
-- **27 – [Concelier CCCS Connector Operations](ops/concelier-cccs-operations.md)**
-- **28 – [Concelier CISA ICS Connector Operations](ops/concelier-icscisa-operations.md)**
-- **29 – [Concelier CERT-Bund Connector Operations](ops/concelier-certbund-operations.md)**
-- **30 – [Concelier MSRC Connector – AAD Onboarding](ops/concelier-msrc-operations.md)**
-
-### Legal & licence
-- **31 – [Legal & Quota FAQ](29_LEGAL_FAQ_QUOTA.md)**
+- **24 – [Offline Update Kit Admin Guide](24_OFFLINE_KIT.md)**
+- **25 – [Mirror Operations Runbook](ops/concelier-mirror-operations.md)**
+- **26 – [Concelier Apple Connector Operations](ops/concelier-apple-operations.md)**
+- **27 – [Authority Key Rotation Playbook](ops/authority-key-rotation.md)**
+- **28 – [Concelier CCCS Connector Operations](ops/concelier-cccs-operations.md)**
+- **29 – [Concelier CISA ICS Connector Operations](ops/concelier-icscisa-operations.md)**
+- **30 – [Concelier CERT-Bund Connector Operations](ops/concelier-certbund-operations.md)**
+- **31 – [Concelier MSRC Connector – AAD Onboarding](ops/concelier-msrc-operations.md)**
+
+### Legal & licence
+- **32 – [Legal & Quota FAQ](29_LEGAL_FAQ_QUOTA.md)**
 
 </details>