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>

go.mod

@@ -0,0 +1,21 @@
+module github.com/cdnutter/playlink
+
+go 1.27.1
+
+require (
+	github.com/go-chi/chi/v5 v5.3.2
+	golang.org/x/crypto v0.57.0
+	modernc.org/sqlite v1.59.0
+)
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/mattn/go-isatty v0.0.24 // indirect
+	github.com/ncruces/go-strftime v1.0.0 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	golang.org/x/sys v0.48.0 // indirect
+	modernc.org/libc v1.75.7 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.12.1 // indirect
+)