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/dev/authority-plugin-di-coordination.md

@@ -0,0 +1,52 @@
+# Authority Plug-in Scoped Service Coordination
+
+> Created: 2025-10-19 — Plugin Platform Guild & Authority Core  
+> Status: Scheduled (session confirmed for 2025-10-20 15:00–16:00 UTC)
+
+This document tracks preparation, agenda, and outcomes for the scoped-service workshop required before implementing PLUGIN-DI-08-002.
+
+## Objectives
+
+- Inventory Authority plug-in surfaces that need scoped service lifetimes.
+- Confirm session/scope handling for identity-provider registrars and background jobs.
+- Assign follow-up tasks/actions with owners and due dates.
+
+## Scheduling Snapshot
+
+- **Meeting time:** 2025-10-20 15:00–16:00 UTC (10:00–11:00 CDT / 08:00–09:00 PDT).
+- **Facilitator:** Plugin Platform Guild — Alicia Rivera.
+- **Attendees (confirmed):** Authority Core — Jasmin Patel; Authority Security Guild — Mohan Singh; Plugin Platform — Alicia Rivera, Leah Chen.
+- **Optional invitees:** DevOps liaison — Sofia Ortega (accepted).
+- **Logistics:** Invites sent via shared calendar on 2025-10-19 15:30 UTC with Teams bridge + offline dial-in. Meeting notes will be captured here.
+- **Preparation deadline:** 2025-10-20 12:00 UTC — complete checklist below.
+
+## Pre-work Checklist
+
+- Review `ServiceBindingAttribute` contract introduced by PLUGIN-DI-08-001.
+- Collect existing Authority plug-in registration code paths to evaluate.
+- Audit background jobs that assume singleton lifetimes.
+- Identify plug-in health checks/telemetry surfaces impacted by scoped lifetimes.
+
+### Pre-work References
+
+- _Add links, file paths, or notes here prior to the session._
+
+## Draft Agenda
+
+1. Context recap (5 min) — why scoped DI is needed; summary of PLUGIN-DI-08-001 changes.
+2. Authority plug-in surfaces (15 min) — registrars, background services, telemetry.
+3. Session handling strategy (10 min) — scope creation semantics, cancellation propagation.
+4. Action items & owners (10 min) — capture code/docs/test tasks with due dates.
+5. Risks & follow-ups (5 min) — dependencies, rollout sequencing.
+
+## Notes
+
+- _Pending coordination session; populate afterwards._
+
+## Action Item Log
+
+| Item | Owner | Due | Status | Notes |
+|------|-------|-----|--------|-------|
+| Confirm meeting time | Alicia Rivera | 2025-10-19 15:30 UTC | DONE | Calendar invite sent; all required attendees accepted |
+| Compile Authority plug-in DI entry points | Jasmin Patel | 2025-10-20 | IN PROGRESS | Gather current Authority plug-in registrars, background jobs, and helper factories that assume singleton lifetimes; add the list with file paths to **Pre-work References** in this document before 2025-10-20 12:00 UTC. |
+| Outline scoped-session pattern for background jobs | Leah Chen | Post-session | BLOCKED | Requires meeting outcomes |