kept data: the choice at reinstall, the list, the read-only view, the load (09 decision 36); R-690 fixed

An install over an app's kept drive folder (appdata/<app> non-empty) asks the household:
"use my kept data" (a load from the newest copy of THIS drive's install, own unit or
second-drive mirror, then the template's after_load) or "start fresh" (the folder is
renamed into <drive>/kept/<app>/<date>/ with the removed app's unit; nothing deleted).
The install API answers 409 kept_data_choice until one is chosen; DeployStack refuses
too. New page Megorzott adatok / Kept data (/kept-data): Load / Look / Delete (typed
confirmation, the only deletion of kept data). FileBrowser gets a read-only source.
The drive-full warning names the kept folders. <drive>/kept is protected and outside
every backup leg.

R-690: the removed-app restore (R-487) never found a unit on a DATA drive — it asked
GetStackComposePath (true for every catalog app) and restored nextcloud with no env.
Now isStackDeployed; pinned with a production-shaped provider.

Red-proofs: audits/night-2026-09-26/E/redproofs/.

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 +22,9 @@ var (
 	ErrPathMissing = errors.New("path field does not exist")
 	// ErrNotEnoughMemory — the memory verdict refused the deploy (API: 400).
 	ErrNotEnoughMemory = errors.New("not enough memory")
+	// ErrKeptDataChoice — the app's drive folder already holds old data and the install named neither
+	// „use my kept data" nor „start fresh" (`09` §3 decision 36; API: 409 with code kept_data_choice).
+	ErrKeptDataChoice = errors.New("kept data: a choice is needed")
 	// 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