AI codebase review

fix: duplicate search no longer hangs on files swapped for FIFOs

Candidates were reopened by path with os.Open after the scan. A file
replaced by a FIFO (or a symlink to one) blocked open(2) forever, and
context cancellation could not interrupt it, wedging the duplicate view
and --duplicates. Content is now opened with O_NOFOLLOW|O_NONBLOCK on
Unix; the existing regular-file check then skips it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/duplicate/duplicate.go

@@ -18,6 +18,7 @@ import (
 	"sync/atomic"
 
 	"github.com/andydixon/mapsize/internal/inventory"
+	"github.com/andydixon/mapsize/internal/platform"
 )
 
 // Group is a set of files verified to have identical content.
@@ -226,7 +227,7 @@ func (f *Finder) splitHash(ctx context.Context, g []cand, workers int) []fullGro
 
 // open opens a candidate and checks it still has the inventoried size.
 func open(c cand) (*os.File, bool) {
-	fh, err := os.Open(c.path)
+	fh, err := platform.OpenContent(c.path)
 	if err != nil {
 		return nil, false
 	}