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.

src/StellaOps.Concelier.Connector.CertBund/TASKS.md

@@ -10,3 +10,4 @@
 |FEEDCONN-CERTBUND-02-007 Feed history & locale assessment|BE-Conn-CERTBUND|Research|**DONE (2025-10-15)** – Measured RSS retention (~6 days/≈250 items), captured connector-driven backfill guidance in the runbook, and aligned locale guidance (preserve `language=de`, Docs glossary follow-up). **Next:** coordinate with Tools to land the state-seeding helper so scripted backfills replace manual Mongo tweaks.|
 |FEEDCONN-CERTBUND-02-008 Session bootstrap & cookie strategy|BE-Conn-CERTBUND|Source.Common|**DONE (2025-10-14)** – Feed client primes the portal session (cookie container via `SocketsHttpHandler`), shares cookies across detail requests, and documents bootstrap behaviour in options (`PortalBootstrapUri`).|
 |FEEDCONN-CERTBUND-02-009 Offline Kit export packaging|BE-Conn-CERTBUND, Docs|Offline Kit|**DONE (2025-10-17)** – Added `tools/certbund_offline_snapshot.py` to capture search/export JSON, emit deterministic manifests + SHA files, and refreshed docs (`docs/ops/concelier-certbund-operations.md`, `docs/24_OFFLINE_KIT.md`) with offline-kit instructions and manifest layout guidance. Seed data README/ignore rules cover local snapshot hygiene.|
+|FEEDCONN-CERTBUND-02-010 Normalized range translator|BE-Conn-CERTBUND|Merge coordination (`FEEDMERGE-COORD-02-900`)|**TODO (due 2025-10-22)** – Translate `product.Versions` phrases (e.g., `2023.1 bis 2024.2`, `alle`) into comparator strings for `SemVerRangeRuleBuilder`, emit `NormalizedVersions` with `certbund:{advisoryId}:{vendor}` provenance, and extend tests/README with localisation notes.|