Adopt sneak.berlin/go/vaultik vanity import path, README overhaul

Module path changed from git.eeqj.de/sneak/vaultik to
sneak.berlin/go/vaultik (vanity redirect). All imports, ldflags,
Dockerfile, goreleaser config, and docs updated. App data/config
directories now use plain "vaultik" instead of the reverse-DNS name.

README:
- New copy-pasteable quickstart at top: go install, config init,
  age keypair, config set for key + file:// destination, home backup
- All command names in command details are code-quoted
- config set/get gained sequence index support (age_recipients.0)
  so lists are settable from the CLI
- Dockerfile build is CGO_ENABLED=0 to match the pure-Go build

internal/cli/app.go

@@ -10,16 +10,16 @@ import (
 	"syscall"
 	"time"
 
-	"git.eeqj.de/sneak/vaultik/internal/config"
-	"git.eeqj.de/sneak/vaultik/internal/database"
-	"git.eeqj.de/sneak/vaultik/internal/globals"
-	"git.eeqj.de/sneak/vaultik/internal/log"
-	"git.eeqj.de/sneak/vaultik/internal/pidlock"
-	"git.eeqj.de/sneak/vaultik/internal/snapshot"
-	"git.eeqj.de/sneak/vaultik/internal/storage"
-	"git.eeqj.de/sneak/vaultik/internal/vaultik"
 	"github.com/adrg/xdg"
 	"go.uber.org/fx"
+	"sneak.berlin/go/vaultik/internal/config"
+	"sneak.berlin/go/vaultik/internal/database"
+	"sneak.berlin/go/vaultik/internal/globals"
+	"sneak.berlin/go/vaultik/internal/log"
+	"sneak.berlin/go/vaultik/internal/pidlock"
+	"sneak.berlin/go/vaultik/internal/snapshot"
+	"sneak.berlin/go/vaultik/internal/storage"
+	"sneak.berlin/go/vaultik/internal/vaultik"
 )
 
 // AppOptions contains common options for creating the fx application.
@@ -125,7 +125,7 @@ func RunApp(ctx context.Context, app *fx.App) error {
 // It acquires a PID lock before starting to prevent concurrent instances.
 func RunWithApp(ctx context.Context, opts AppOptions) error {
 	// Acquire PID lock to prevent concurrent instances
-	lockDir := filepath.Join(xdg.DataHome, "berlin.sneak.app.vaultik")
+	lockDir := filepath.Join(xdg.DataHome, "vaultik")
 	lock, err := pidlock.Acquire(lockDir)
 	if err != nil {
 		if errors.Is(err, pidlock.ErrAlreadyRunning) {