Implement upgrade.sh for framework version upgrades

Removes old framework files (per current file-list), copies in new
ones from the target ref, and stages everything for the user to
review before committing. Also adds file-list to itself so it
gets upgraded too.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

file-list

@@ -5,10 +5,12 @@ backend/package.json
 backend/pnpm-workspace.yaml
 # express/framework
 cmd
+file-list
 develop
 diachron
 logger
 master
 mgmt
 sync.sh
-templates
+templates
+upgrade.sh