chore: fix server-install.sh and update .env for Grav 2.0 production deploy

- server-install.sh: use GitHub releases URL (avoids channel suffix hack)
- GRAV_VERSION bumped to 2.0.0-rc.10 in .env.example
- production-todo.md: mark Phase 2.1 env vars as done

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vgmzx8VTTTmCskSpQtsLTr

scripts/server-install.sh

@@ -22,7 +22,7 @@ chmod 600 ~/.netrc
 
 echo "==> Downloading Grav $GRAV_VERSION"
 cd "$WEBROOT"
-wget --no-verbose "https://getgrav.org/download/core/grav-admin/${GRAV_VERSION}${GRAV_CHANNEL_SUFFIX:-}" -O grav-admin.zip
+wget --no-verbose "https://github.com/getgrav/grav/releases/download/${GRAV_VERSION}/grav-admin-v${GRAV_VERSION}.zip" -O grav-admin.zip
 unzip -oq grav-admin.zip
 cp -rf grav-admin/. .
 cp -rf grav-admin/user/plugins/admin2 /tmp/admin2-plugin