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/web/server.go

@@ -632,6 +632,12 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		s.settingsHandler(w, r)
 	case path == "/storage" && r.Method == http.MethodGet:
 		s.storagePageHandler(w, r)
+	case path == "/kept-data" && r.Method == http.MethodGet:
+		s.keptPageHandler(w, r)
+	case path == "/kept-data/delete" && r.Method == http.MethodPost:
+		s.keptDeleteHandler(w, r)
+	case path == "/kept-data/load" && r.Method == http.MethodPost:
+		s.keptLoadHandler(w, r)
 	case path == "/storage/network" && r.Method == http.MethodGet:
 		s.storageNetworkPageHandler(w, r)
 	// „Megosztás" — LAN network sharing (R-7 slice 1)