refactor: split store.go into focused files by responsibility (task o6)

Split 562-line store.go into four files:
- store.go (264 lines): Store type, WalkIndexes, Search, action dispatch
- store_crud.go (160 lines): Add, Import, Remove, buildPair
- store_picker.go (160 lines): Fzf, PickerResult, key parsing
- store_shred.go (54 lines): ShredFile, ShredAllExported

No API or behaviour changes. All functions under 30 lines, all files under 300 lines.

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

1 files changed, 54 insertions, 0 deletions

diff --git a/internal/store/store_shred.go b/internal/store/store_shred.go
new file mode 100644
index 0000000..7d28f70
--- /dev/null
+++ b/internal/store/store_shred.go
@@ -0,0 +1,54 @@
+// store_shred.go provides secure file deletion for the secret store.
+// ShredFile uses GNU shred(1) when available and falls back to "rm -Pfv".
+// ShredAllExported iterates cfg.ExportDir and shreds every regular file,
+// mirroring Ruby's Geheim#shred_all_exported best-effort deletion strategy.
+package store
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
+// ShredAllExported removes (shreds) every regular file in cfg.ExportDir.
+// Uses GNU shred when available; falls back to "rm -Pfv" otherwise.
+// Mirrors Ruby's shred_all_exported: iterates all files and returns the last
+// non-nil error so that as many files as possible are shredded even on failure.
+func (s *Store) ShredAllExported(ctx context.Context) error {
+	entries, err := filepath.Glob(filepath.Join(s.cfg.ExportDir, "*"))
+	if err != nil {
+		return fmt.Errorf("listing export dir: %w", err)
+	}
+
+	var lastErr error
+	for _, entry := range entries {
+		info, err := os.Stat(entry)
+		if err != nil || !info.Mode().IsRegular() {
+			continue
+		}
+		if err := ShredFile(ctx, entry); err != nil {
+			// Record the error but keep shredding — security demands best-effort
+			// destruction of all exported secrets even if one fails.
+			lastErr = err
+		}
+	}
+	return lastErr
+}
+
+// ShredFile destroys a single file using shred(1) if available, or rm -Pfv.
+// This mirrors Ruby's Geheim#shred_file method.
+func ShredFile(ctx context.Context, filePath string) error {
+	if _, err := exec.LookPath("shred"); err == nil {
+		cmd := exec.CommandContext(ctx, "shred", "-vu", filePath)
+		cmd.Stdout = io.Discard
+		cmd.Stderr = io.Discard
+		return cmd.Run()
+	}
+	cmd := exec.CommandContext(ctx, "rm", "-Pfv", filePath)
+	cmd.Stdout = io.Discard
+	cmd.Stderr = io.Discard
+	return cmd.Run()
+}