chore: STAGING_PATH entfernt, ci-starter-defaults für Template-Staging

- STAGING_PATH aus .env und Makefile (media-sync-local-to-staging) entfernt, Doku bereinigt
- scripts/ci-starter-defaults.sh löst __PLACEHOLDER__ im CI-Workspace auf, dev/master bleiben identisch

.agents/skills/deployment/SKILL.md

@@ -87,9 +87,6 @@ PRODUCTION_SERVER=dock4.basehosts.de
 PRODUCTION_TIBI_PREFIX=tibi
 PRODUCTION_PATH=/webroots2/customers/<customer-id>/htdocs
 
-# Staging
-STAGING_PATH=/staging/<org>/<project>/dev
-
 # URLs
 LIVE_URL=http://<subdomain>.<domain>.dock4.basispanel.de   # Preview-URL
 STAGING_URL=https://dev-<project>.staging.testversion.online

.agents/skills/tibi-project-setup/SKILL.md

@@ -119,7 +119,7 @@ Important:
 - if `GET /api/v1/project` with `X-Admin-Token: $ADMIN_TOKEN` returns `permission denied: admin token lacks permission project.read`, that token is not valid for project registration
 - create new projects by logging in with `admin` / `admin` in the default starter dev setup and using the returned JWT via `X-Auth-Token`
 - `ADMIN_ASSET_VERSION` is required so Nova picks up the current admin bundle
-- `PROJECT_NAME`, `TIBI_NAMESPACE`, `PRODUCTION_PATH`, and `STAGING_PATH` should be project-specific before the first deploy
+- `PROJECT_NAME`, `TIBI_NAMESPACE`, and `PRODUCTION_PATH` should be project-specific before the first deploy
 - `package.json` should no longer advertise the starter repository or default package name once the project is bootstrapped
 
 ## Step 4 — Install and start the Docker stack