v0.26.0: Storage namespace felhom-data/ + test node wipe script

All felhom-managed data on external drives now lives under felhom-data/
subdirectory, cleanly separating controller data from user files.

- backup/paths.go: add FelhomDataDir constant, update 8 path helpers
- stacks/delete.go: add local felhomDataDir constant (circular import
  boundary), update ProtectedHDDPaths + GetStackBackupData
- storage/migrate_drive.go: import backup pkg, fix conflict check, verify,
  rsync excludes (felhom-data/backups/*/restic/), size estimation
- storage/migrate.go: import backup pkg, fix DB dump paths
- web/handlers.go: fix legacy 'storage' path -> backup.AppDataDir()
- storage/format_linux.go: create felhom-data/ instead of storage/
- storage/attach_linux.go: create felhom-data/ instead of storage/
- scripts/felhom-wipe.sh: new multi-level test node wipe script
  (soft/controller/full/nuclear)
- CHANGELOG.md, controller/README.md, scripts/README.md: updated docs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

controller/internal/backup/paths.go

@@ -2,44 +2,47 @@ package backup
 
 import "path/filepath"
 
+// FelhomDataDir is the namespace directory on storage drives for all felhom-managed data.
+const FelhomDataDir = "felhom-data"
+
 // PrimaryBackupPath returns the root primary backup directory for a drive.
 func PrimaryBackupPath(drivePath string) string {
-	return filepath.Join(drivePath, "backups", "primary")
+	return filepath.Join(drivePath, FelhomDataDir, "backups", "primary")
 }
 
 // PrimaryResticRepoPath returns the restic repo path on a drive's primary backup.
 func PrimaryResticRepoPath(drivePath string) string {
-	return filepath.Join(drivePath, "backups", "primary", "restic")
+	return filepath.Join(drivePath, FelhomDataDir, "backups", "primary", "restic")
 }
 
 // AppDBDumpPath returns the DB dump directory for an app on its home drive.
 func AppDBDumpPath(drivePath, stackName string) string {
-	return filepath.Join(drivePath, "backups", "primary", stackName, "db-dumps")
+	return filepath.Join(drivePath, FelhomDataDir, "backups", "primary", stackName, "db-dumps")
 }
 
 // SecondaryBackupPath returns the root secondary backup directory for a drive.
 func SecondaryBackupPath(drivePath string) string {
-	return filepath.Join(drivePath, "backups", "secondary")
+	return filepath.Join(drivePath, FelhomDataDir, "backups", "secondary")
 }
 
 // AppSecondaryRsyncPath returns the rsync destination for an app's secondary backup.
 func AppSecondaryRsyncPath(drivePath, stackName string) string {
-	return filepath.Join(drivePath, "backups", "secondary", stackName, "rsync")
+	return filepath.Join(drivePath, FelhomDataDir, "backups", "secondary", stackName, "rsync")
 }
 
 // SecondaryResticRepoPath returns the restic repo path on a drive's secondary backup.
 func SecondaryResticRepoPath(drivePath string) string {
-	return filepath.Join(drivePath, "backups", "secondary", "restic")
+	return filepath.Join(drivePath, FelhomDataDir, "backups", "secondary", "restic")
 }
 
 // SecondaryInfraPath returns the infrastructure config mirror directory on a drive's secondary backup.
 func SecondaryInfraPath(drivePath string) string {
-	return filepath.Join(drivePath, "backups", "secondary", "_infra")
+	return filepath.Join(drivePath, FelhomDataDir, "backups", "secondary", "_infra")
 }
 
 // AppDataDir returns the app data directory path on a drive.
 func AppDataDir(drivePath, stackName string) string {
-	return filepath.Join(drivePath, "appdata", stackName)
+	return filepath.Join(drivePath, FelhomDataDir, "appdata", stackName)
 }
 
 // InfraBackupDir returns the hidden infra backup directory on a drive.