Add pluggable storage backend, PID locking, and improved scan progress

Storage backend:
- Add internal/storage package with Storer interface
- Implement FileStorer for local filesystem storage (file:// URLs)
- Implement S3Storer wrapping existing s3.Client
- Support storage_url config field (s3:// or file://)
- Migrate all consumers to use storage.Storer interface

PID locking:
- Add internal/pidlock package to prevent concurrent instances
- Acquire lock before app start, release on exit
- Detect stale locks from crashed processes

Scan progress improvements:
- Add fast file enumeration pass before stat() phase
- Use enumerated set for deletion detection (no extra filesystem access)
- Show progress with percentage, files/sec, elapsed time, and ETA
- Change "changed" to "changed/new" for clarity

Config improvements:
- Add tilde expansion for paths (~/)
- Use xdg library for platform-specific default index path

internal/cli/store.go

@@ -7,14 +7,14 @@ import (
 	"time"
 
 	"git.eeqj.de/sneak/vaultik/internal/log"
-	"git.eeqj.de/sneak/vaultik/internal/s3"
+	"git.eeqj.de/sneak/vaultik/internal/storage"
 	"github.com/spf13/cobra"
 	"go.uber.org/fx"
 )
 
 // StoreApp contains dependencies for store commands
 type StoreApp struct {
-	S3Client   *s3.Client
+	Storage    storage.Storer
 	Shutdowner fx.Shutdowner
 }
 
@@ -48,19 +48,18 @@ func newStoreInfoCommand() *cobra.Command {
 
 // Info displays storage information
 func (app *StoreApp) Info(ctx context.Context) error {
-	// Get bucket info
-	bucketName := app.S3Client.BucketName()
-	endpoint := app.S3Client.Endpoint()
+	// Get storage info
+	storageInfo := app.Storage.Info()
 
 	fmt.Printf("Storage Information\n")
 	fmt.Printf("==================\n\n")
-	fmt.Printf("S3 Configuration:\n")
-	fmt.Printf("  Endpoint: %s\n", endpoint)
-	fmt.Printf("  Bucket:   %s\n\n", bucketName)
+	fmt.Printf("Storage Configuration:\n")
+	fmt.Printf("  Type:     %s\n", storageInfo.Type)
+	fmt.Printf("  Location: %s\n\n", storageInfo.Location)
 
 	// Count snapshots by listing metadata/ prefix
 	snapshotCount := 0
-	snapshotCh := app.S3Client.ListObjectsStream(ctx, "metadata/", true)
+	snapshotCh := app.Storage.ListStream(ctx, "metadata/")
 	snapshotDirs := make(map[string]bool)
 
 	for object := range snapshotCh {
@@ -79,7 +78,7 @@ func (app *StoreApp) Info(ctx context.Context) error {
 	blobCount := 0
 	var totalSize int64
 
-	blobCh := app.S3Client.ListObjectsStream(ctx, "blobs/", false)
+	blobCh := app.Storage.ListStream(ctx, "blobs/")
 	for object := range blobCh {
 		if object.Err != nil {
 			return fmt.Errorf("listing blobs: %w", object.Err)
@@ -130,10 +129,9 @@ func runWithApp(ctx context.Context, fn func(*StoreApp) error) error {
 			Debug:   rootFlags.Debug,
 		},
 		Modules: []fx.Option{
-			s3.Module,
-			fx.Provide(func(s3Client *s3.Client, shutdowner fx.Shutdowner) *StoreApp {
+			fx.Provide(func(storer storage.Storer, shutdowner fx.Shutdowner) *StoreApp {
 				return &StoreApp{
-					S3Client:   s3Client,
+					Storage:    storer,
 					Shutdowner: shutdowner,
 				}
 			}),