Remove remaining OS-specific hardcodes from core scripts

OS version reads now go through platform_get_os_version() and
platform_os_version_probe_cmd() instead of grepping /etc/unraid-version directly.

STATE_DIR fallbacks to /boot/config removed — STATE_DIR is always set by
load_config.sh and the fallback encoded a platform-specific path.

Setup DB path references use platform_setup_db_path() instead of the
VARAVERK_SETUP_FILE/-/boot/config compound fallback.

DOCKER_APPDATA_BASE default removed from arr_sync.sh — the adapter sets it.

Fallback/fallback_test.sh

@@ -185,13 +185,13 @@ log "$ICON_GEAR Config: remote=${REMOTE_SERVER_NAME} (${REMOTE_SERVER}) fallback
 # ━━━ Status ━━━
 # ==============================================================================================
 if [[ "$SHOW_STATUS" == true ]]; then
-    local_ver=$(grep -oP '(?<=version=")[^"]+' /etc/unraid-version 2>/dev/null || echo "unknown")
+    local_ver=$(platform_get_os_version 2>/dev/null || echo "unknown")
 
     echo ""
     echo "━━━━━ $ICON_SUMMARY STATUS ━━━━━"
     echo "$ICON_HOST      My ID:         $MY_ID ($LOCAL_SERVER_NAME)"
     echo "$ICON_HOST      Remote ID:     $REMOTE_ID ($REMOTE_SERVER_NAME — $REMOTE_SERVER)"
-    echo "$ICON_GEAR      unRAID ver:    $local_ver"
+    echo "$ICON_GEAR      OS ver:        $local_ver"
     echo "$ICON_FALLBACK  Block wait:    ${FALLBACK_TEST_BLOCK_WAIT}s"
     echo "$ICON_FALLBACK  Handback wait: ${FALLBACK_TEST_HANDBACK_WAIT}s"
     echo "$ICON_FALLBACK  Check interval: ${FALLBACK_CHECK_INTERVAL}s"