Platform-agnostic refactor: eliminate OS-specific hardcodes from core scripts

All bash scripts are now platform-neutral. Unraid-specific paths, commands,
and service checks moved to Plugin/unraid/adapter.sh. Core scripts call
platform_*() functions exclusively — no direct OS paths in runtime logic.

New adapter functions: platform_storage_path, platform_webui_install_path,
platform_scripts_dir_probe_cmd, platform_setup_db_path, platform_storage_healthy,
platform_is_service_enabled, platform_get_temp_thresholds, platform_disk_states_path,
platform_rebuild_container, platform_push_conf, platform_push_setup_state,
platform_get_templates_dir, platform_send_os_notification.

Partnership services stack (Emby/Jellyfin/Seerr/SeerrFin) added as third
onboarding stack alongside auth and arr stacks.

Watchdogs/docker_watchdog.sh

@@ -254,12 +254,6 @@ fi
 log "$ICON_GEAR Config: grace=${WATCHDOG_STARTUP_GRACE}s mem-soft=${SOFT_MEM_THRESHOLD}% cpu-soft=${SOFT_CPU_THRESHOLD}% cpu-hard=${HARD_CPU_THRESHOLD}% cpu-limit=${CPU_FAIL_LIMIT} http-limit=${RESP_FAIL_LIMIT} daemon-timeout=${DOCKER_TIMEOUT}s"
 log "$ICON_CONTAINERS Tier1:  watched=${#WATCHDOG_CONTAINERS[@]} required=${#WATCHDOG_REQUIRED_CONTAINERS[@]} urls=${#WATCHDOG_CONTAINER_URLS[@]} restart-limit=${WATCHDOG_CONTAINER_RESTART_LIMIT}/${WATCHDOG_CONTAINER_RESTART_WINDOW}h"
 
-# Validate unRAID-specific commands used by this script
-# If rc.docker is missing or changed, daemon restart will fail — better to know now
-platform_require_cmd     "/etc/rc.d/rc.docker"     ""     ""     "Docker rc.d script" || warn "rc.docker not found — daemon restart unavailable if needed"
-
-platform_require_cmd     "/usr/local/emhttp/plugins/dynamix/scripts/notify"     ""     ""     "unRAID notify script" || warn "unRAID notify script not found — native notifications disabled"
-
 # Ensure state files exist
 touch "$WATCHDOG_STATE_FILE" "$WATCHDOG_CONTAINER_RESTART_LOG" \
       "$DOCKER_WATCHDOG_FAILED_FILE" 2>/dev/null