Ops: add Proxmox migration tooling and runbook

Add end-to-end migration scripts for inventory, precopy, cutover, smoke tests, rollback, and post-migration checks. Include an operational runbook and Proxmox env template to move Hördle behind Nginx Proxy Manager while preserving persistent volumes safely.

.env.proxmox.example

@@ -0,0 +1,29 @@
+# ============================================
+# Hördle Environment (Proxmox + NPM)
+# ============================================
+# Kopiere nach .env und passe alle Werte an.
+
+# Build-Time
+NEXT_PUBLIC_APP_NAME=Hördle
+NEXT_PUBLIC_APP_DESCRIPTION=Daily music guessing game
+NEXT_PUBLIC_DOMAIN=hoerdle.de
+NEXT_PUBLIC_TWITTER_HANDLE=@hoerdle
+NEXT_PUBLIC_PLAUSIBLE_DOMAIN=hoerdle.de
+NEXT_PUBLIC_PLAUSIBLE_SCRIPT_SRC=https://plausible.example.com/js/script.js
+NEXT_PUBLIC_THEME_COLOR=#000000
+NEXT_PUBLIC_BACKGROUND_COLOR=#ffffff
+NEXT_PUBLIC_CREDITS_ENABLED=true
+NEXT_PUBLIC_CREDITS_TEXT=Vibe coded with coffee
+NEXT_PUBLIC_CREDITS_LINK_TEXT=@yourhandle@server.social
+NEXT_PUBLIC_CREDITS_LINK_URL=https://server.social/@yourhandle
+
+# Runtime
+DATABASE_URL=file:/app/data/prod.db
+ADMIN_PASSWORD=<BCRYPT_HASH_HERE>
+TZ=Europe/Berlin
+GOTIFY_URL=
+GOTIFY_APP_TOKEN=
+OPENROUTER_API_KEY=
+
+# Optional Build Metadata
+# APP_VERSION=v1.0.0