Initial commit: playlink music library hardlink deduplicator

Go backend (chi, SQLite) with an embedded React/TypeScript UI that finds
songs present in both a host and a slave music library and replaces the
slave copy with a hardlink to the host copy.

- Path-first matching with format/title/album-folder fallbacks
- Auto-linking of byte-identical files, re-verified with cmp before linking
- Manual review with ffprobe quality comparison, downgrade guard and
  promote-to-host override
- Build mode to populate an empty slave library from the host
- Dry run by default, atomic stage+rename replacement, quarantine with
  retention, undo, path confinement and authenticated UI
- Dockerfile and compose file for Unraid

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

web/embed.go

@@ -0,0 +1,19 @@
+// Package web embeds the built single-page app.
+package web
+
+import (
+	"embed"
+	"io/fs"
+)
+
+//go:embed all:dist
+var dist embed.FS
+
+// Dist returns the built UI rooted at dist/.
+func Dist() fs.FS {
+	sub, err := fs.Sub(dist, "dist")
+	if err != nil {
+		panic(err)
+	}
+	return sub
+}