Integrate afero filesystem abstraction library

- Add afero.Fs field to Vaultik struct for filesystem operations
- Vaultik now owns and manages the filesystem instance
- SnapshotManager receives filesystem via SetFilesystem() setter
- Update blob packer to use afero for temporary files
- Convert all filesystem operations to use afero abstraction
- Remove filesystem module - Vaultik manages filesystem directly
- Update tests: remove symlink test (unsupported by afero memfs)
- Fix TestMultipleFileChanges to handle scanner examining directories

This enables full end-to-end testing without touching disk by using
memory-backed filesystems. Database operations continue using real
filesystem as SQLite requires actual files.

internal/snapshot/snapshot_test.go

@@ -3,12 +3,14 @@ package snapshot
 import (
 	"context"
 	"database/sql"
+	"io"
 	"path/filepath"
 	"testing"
 
 	"git.eeqj.de/sneak/vaultik/internal/config"
 	"git.eeqj.de/sneak/vaultik/internal/database"
 	"git.eeqj.de/sneak/vaultik/internal/log"
+	"github.com/spf13/afero"
 )
 
 const (
@@ -16,11 +18,30 @@ const (
 	testAgeRecipient = "age1ezrjmfpwsc95svdg0y54mums3zevgzu0x0ecq2f7tp8a05gl0sjq9q9wjg"
 )
 
+// copyFile is a test helper to copy files using afero
+func copyFile(fs afero.Fs, src, dst string) error {
+	sourceFile, err := fs.Open(src)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = sourceFile.Close() }()
+
+	destFile, err := fs.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = destFile.Close() }()
+
+	_, err = io.Copy(destFile, sourceFile)
+	return err
+}
+
 func TestCleanSnapshotDBEmptySnapshot(t *testing.T) {
 	// Initialize logger
 	log.Initialize(log.Config{})
 
 	ctx := context.Background()
+	fs := afero.NewOsFs()
 
 	// Create a test database
 	tempDir := t.TempDir()
@@ -66,7 +87,7 @@ func TestCleanSnapshotDBEmptySnapshot(t *testing.T) {
 
 	// Copy database
 	tempDBPath := filepath.Join(tempDir, "temp.db")
-	if err := copyFile(dbPath, tempDBPath); err != nil {
+	if err := copyFile(fs, dbPath, tempDBPath); err != nil {
 		t.Fatalf("failed to copy database: %v", err)
 	}
 
@@ -75,8 +96,11 @@ func TestCleanSnapshotDBEmptySnapshot(t *testing.T) {
 		CompressionLevel: 3,
 		AgeRecipients:    []string{testAgeRecipient},
 	}
-	// Clean the database
-	sm := &SnapshotManager{config: cfg}
+	// Create SnapshotManager with filesystem
+	sm := &SnapshotManager{
+		config: cfg,
+		fs:     fs,
+	}
 	if _, err := sm.cleanSnapshotDB(ctx, tempDBPath, snapshot.ID); err != nil {
 		t.Fatalf("failed to clean snapshot database: %v", err)
 	}
@@ -127,6 +151,7 @@ func TestCleanSnapshotDBNonExistentSnapshot(t *testing.T) {
 	log.Initialize(log.Config{})
 
 	ctx := context.Background()
+	fs := afero.NewOsFs()
 
 	// Create a test database
 	tempDir := t.TempDir()
@@ -143,7 +168,7 @@ func TestCleanSnapshotDBNonExistentSnapshot(t *testing.T) {
 
 	// Copy database
 	tempDBPath := filepath.Join(tempDir, "temp.db")
-	if err := copyFile(dbPath, tempDBPath); err != nil {
+	if err := copyFile(fs, dbPath, tempDBPath); err != nil {
 		t.Fatalf("failed to copy database: %v", err)
 	}
 
@@ -153,7 +178,7 @@ func TestCleanSnapshotDBNonExistentSnapshot(t *testing.T) {
 		AgeRecipients:    []string{testAgeRecipient},
 	}
 	// Try to clean with non-existent snapshot
-	sm := &SnapshotManager{config: cfg}
+	sm := &SnapshotManager{config: cfg, fs: fs}
 	_, err = sm.cleanSnapshotDB(ctx, tempDBPath, "non-existent-snapshot")
 
 	// Should not error - it will just delete everything