feat: add mergerfs mover and snapraid integration

New 'Almacenamiento' page with:
- Auto-detection of rsync, mergerfs, snapraid binaries and mergerfs mount
- Configurable pool settings (source/dest, macOS cleanup, rsync flags)
- Mergerfs mover with dry-run preview and live SSE output streaming
- SnapRAID diff/sync/scrub/check with live SSE output
- Async job system (1 concurrent job) with SSE streaming
- Job history table

Backend:
- internal/storage/ package with capabilities, mergerfs, snapraid, jobs
- storage_config and storage_jobs DB tables (migration 0008)
- GET/PUT /api/storage/config, GET /api/storage/capabilities
- POST/GET /api/storage/jobs, GET /api/storage/jobs/{id}/stream
- Storage operations disabled when NASCTL_EXEC_SYSTEM=false

Closes #new-feature

internal/storage/snapraid_test.go

@@ -0,0 +1,104 @@
+package storage
+
+import "testing"
+
+func TestBuildSnapraidArgs(t *testing.T) {
+	tests := []struct {
+		kind string
+		cfg  SnapraidConfig
+		want []string
+	}{
+		{
+			"snapraid_diff",
+			SnapraidConfig{Content: "/pool/snapraid.content"},
+			[]string{"snapraid", "-c", "/pool/snapraid.content", "diff"},
+		},
+		{
+			"snapraid_sync",
+			SnapraidConfig{Content: "/pool/snapraid.content"},
+			[]string{"snapraid", "-c", "/pool/snapraid.content", "sync"},
+		},
+		{
+			"snapraid_check",
+			SnapraidConfig{Content: "/pool/snapraid.content"},
+			[]string{"snapraid", "-c", "/pool/snapraid.content", "check"},
+		},
+		{
+			"snapraid_scrub",
+			SnapraidConfig{Content: "/pool/snapraid.content", ScrubPlan: 8},
+			[]string{"snapraid", "-c", "/pool/snapraid.content", "scrub", "-p", "8"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.kind, func(t *testing.T) {
+			got, err := BuildSnapraidArgs(tt.kind, tt.cfg)
+			if err != nil {
+				t.Fatalf("BuildSnapraidArgs: %v", err)
+			}
+			if len(got) != len(tt.want) {
+				t.Errorf("BuildSnapraidArgs = %v, want %v", got, tt.want)
+				return
+			}
+			for i := range got {
+				if got[i] != tt.want[i] {
+					t.Errorf("BuildSnapraidArgs[%d] = %q, want %q", i, got[i], tt.want[i])
+				}
+			}
+		})
+	}
+}
+
+func TestBuildSnapraidArgsNoContent(t *testing.T) {
+	_, err := BuildSnapraidArgs("snapraid_sync", SnapraidConfig{Content: ""})
+	if err == nil {
+		t.Error("expected error for empty content")
+	}
+}
+
+func TestValidateScrubPlan(t *testing.T) {
+	tests := []struct {
+		plan  int
+		wantErr bool
+	}{
+		{0, true},
+		{-1, true},
+		{100, true},
+		{1, false},
+		{50, false},
+		{99, false},
+	}
+	for _, tt := range tests {
+		err := ValidateScrubPlan(tt.plan)
+		if tt.wantErr && err == nil {
+			t.Errorf("ValidateScrubPlan(%d) = nil, want error", tt.plan)
+		}
+		if !tt.wantErr && err != nil {
+			t.Errorf("ValidateScrubPlan(%d) = %v, want nil", tt.plan, err)
+		}
+	}
+}
+
+func TestParseSnapraidDataDirs(t *testing.T) {
+	tests := []struct {
+		input string
+		want  []string
+	}{
+		{"", nil},
+		{"/disk1", []string{"/disk1"}},
+		{"/disk1,/disk2", []string{"/disk1", "/disk2"}},
+		{"/disk1, /disk2 , /disk3", []string{"/disk1", "/disk2", "/disk3"}},
+		{"  /disk1  ,  /disk2  ", []string{"/disk1", "/disk2"}},
+	}
+	for _, tt := range tests {
+		got := ParseSnapraidDataDirs(tt.input)
+		if len(got) != len(tt.want) {
+			t.Errorf("ParseSnapraidDataDirs(%q) = %v, want %v", tt.input, got, tt.want)
+			continue
+		}
+		for i := range got {
+			if got[i] != tt.want[i] {
+				t.Errorf("ParseSnapraidDataDirs(%q)[%d] = %q, want %q", tt.input, i, got[i], tt.want[i])
+			}
+		}
+	}
+}