Add Retrospective Extension to community catalog README table (github#1741)

* Add retrospective extension to community catalog.

Register the new retrospective extension release so users can discover and install it from the community catalog.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Add Retrospective Extension to community catalog

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Co-authored-by: Cursor <cursoragent@cursor.com>

Author: 2 people

extensions/README.md

@@ -77,6 +77,7 @@ The following community-contributed extensions are available in [`catalog.commun
 | Spec Sync | Detect and resolve drift between specs and implementation. AI-assisted resolution with human approval | [spec-kit-sync](https://github.com/bgervin/spec-kit-sync) |
 | V-Model Extension Pack | Enforces V-Model paired generation of development specs and test specs with full traceability | [spec-kit-v-model](https://github.com/leocamello/spec-kit-v-model) |
 
+
 ## Adding Your Extension
 
 ### Submission Process