controller v0.265.0: R-634 cause fixed, held apps say so, OOM storm alarm, R-647 leftovers

R-634: a whole-box backup no longer stops/restarts a DEPLOYING app (the
measured cause of containers running under 'not deployed'); StopStack
and StartStack refuse a deploying stack for every caller.
R-625: held badge 'Stopped - restore needed', no Update button.
R-636: kernel oom_kill counter; 20+ in 30 min -> one app_oom_storm.
R-647: held error per reader, copy_holds key, two log wordings.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/stacks/deploy_errors.go

@@ -22,6 +22,11 @@ var (
 	ErrPathMissing = errors.New("path field does not exist")
 	// ErrNotEnoughMemory — the memory verdict refused the deploy (API: 400).
 	ErrNotEnoughMemory = errors.New("not enough memory")
+	// ErrStackDeploying — R-634 (v0.265.0): a stop or start was asked of a stack whose deploy is still
+	// running. Refused, because a `compose down` or a second `compose up -d` in the middle of the
+	// deploy's own `up` makes BOTH fail, and the deploy then records „not deployed" over whatever
+	// containers the race left behind. Pinned by TestR634_StopAndStartRefuseADeployingStack.
+	ErrStackDeploying = errors.New("stack is being deployed")
 )
 
 // msgHU renders a bundle message in Hungarian.