v0.15.0: Attach existing drive wizard (bind mount, no format)

New Settings wizard to attach drives with existing filesystems without
formatting. Mounts partition at staging path, lets user browse and pick
a subfolder, then bind-mounts it at /mnt/<name> with fstab entries.

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

controller/internal/storage/attach_other.go

@@ -0,0 +1,30 @@
+//go:build !linux
+
+package storage
+
+import "fmt"
+
+// MountRaw is not supported on non-Linux platforms.
+func MountRaw(devicePath string) (string, error) {
+	return "", fmt.Errorf("storage attach is only supported on Linux")
+}
+
+// ListDirectories is not supported on non-Linux platforms.
+func ListDirectories(basePath string) ([]DirEntry, error) {
+	return nil, fmt.Errorf("storage attach is only supported on Linux")
+}
+
+// CreateDirectory is not supported on non-Linux platforms.
+func CreateDirectory(basePath, name string) (string, error) {
+	return "", fmt.Errorf("storage attach is only supported on Linux")
+}
+
+// FinalizeAttach is not supported on non-Linux platforms.
+func FinalizeAttach(req AttachRequest, progress chan<- FormatProgress) (string, error) {
+	return "", fmt.Errorf("storage attach is only supported on Linux")
+}
+
+// CleanupRawMount is not supported on non-Linux platforms.
+func CleanupRawMount(rawPath string) error {
+	return fmt.Errorf("storage attach is only supported on Linux")
+}