docs: add core plugin and review skill to README

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

Author: factory-nizar

README.md

@@ -31,8 +31,6 @@ Core skills for essential functionalities and integrations. Pre-installed by the
 **Skills:**
 
 - `review` - Review code changes and identify high-confidence, actionable bugs. Includes systematic analysis patterns for null safety, async/await, security, concurrency, API contracts, and more. Used by both the CLI `/review` command and the CI action.
-- `session-navigation` - Search and navigate past Droid sessions
-- `init` - Session initialization
 
 ### security-engineer