Set container timezone during Proxmox install

Debian LXC templates default to UTC, which made the "hinzugefügt am"
timestamps and export filenames look wrong. Add a TIMEZONE variable
(default Europe/Berlin) applied via timedatectl during install, and
document it in the README.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

scripts/proxmox/install-linkvault.sh

@@ -33,6 +33,7 @@ CT_PASSWORD="${CT_PASSWORD:-}"         # leer = zufällig generiert
 REPO_URL="${REPO_URL:-https://gitea.teamthiele.de/ethiele/linkvault.git}"
 APP_PORT="${APP_PORT:-8000}"
 GIT_TOKEN="${GIT_TOKEN:-}"             # Gitea Access Token, falls Repo privat ist
+TIMEZONE="${TIMEZONE:-Europe/Berlin}"  # wirkt sich auf die angezeigten Datumsangaben aus
 
 # ---------------------------------------------------------------------------
 # Vorbedingungen
@@ -50,6 +51,7 @@ echo "==> Container-ID:      $CTID"
 echo "==> Hostname:           $CT_HOSTNAME"
 echo "==> Storage (RootFS):   $CT_STORAGE"
 echo "==> Netzwerk:           $CT_BRIDGE / $CT_IP"
+echo "==> Zeitzone:           $TIMEZONE"
 
 # ---------------------------------------------------------------------------
 # Debian-12-Template sicherstellen
@@ -114,6 +116,8 @@ export DEBIAN_FRONTEND=noninteractive
 apt-get update -qq
 apt-get install -y -qq git python3 python3-venv python3-pip build-essential curl >/dev/null
 
+timedatectl set-timezone '${TIMEZONE}' || echo 'Warnung: Zeitzone ${TIMEZONE} konnte nicht gesetzt werden.'
+
 if [ ! -d /opt/linkvault ]; then
   if [ -n '${GIT_TOKEN}' ]; then
     git -c http.extraHeader=\"Authorization: token ${GIT_TOKEN}\" clone --quiet '${REPO_URL}' /opt/linkvault