Polish before first GitHub push: consistent adapter usage and naming

stability_watchdog.sh mover check now uses platform_is_mover_running()
instead of raw pgrep, matching server_reboot.sh.

check_unraid_version_parity() renamed to check_os_version_parity() —
the function internals were already platform-neutral after the adapter
refactor; the name was the last Unraid artifact.

Fallback/fallback.sh

@@ -662,7 +662,7 @@ run_handback() {
     echo ""
     echo "━━━ $ICON_SHIELD Pre-flight ━━━"
 
-    if ! check_unraid_version_parity; then
+    if ! check_os_version_parity; then
         warn "Version parity check failed — aborting handback, will retry next cycle"
         state_set handback_strikes 0
         return 1

Fallback/fallback_test.sh

@@ -257,7 +257,7 @@ else
 fi
 
 # Version parity — test may produce misleading results on mismatch
-if ! check_unraid_version_parity; then
+if ! check_os_version_parity; then
     error "unRAID version mismatch — test aborted to prevent misleading results"
     phase_fail "Pre-flight"
     exit 1