feat: implement Havenllo single-board kanban (Go+SQLite backend, Preact/Vite frontend)

- Single fixed 'Haven' board: lists (To do/In progress/Done) + cards, no multi-board
- Go 1.24 backend, CGO-free modernc.org/sqlite, embedded SPA, REST /api
- Preact + Vite + TS frontend, native HTML5 drag-and-drop, optimistic UI, dark Haven theme
- PVC (nfs-client) for SQLite, root container on NFS, simple nginx ingress havenllo.haven
- Dockerfile multi-arch build, Gitea CI via pipeline-actions@main

web/embed.go

@@ -0,0 +1,20 @@
+package web
+
+import (
+	"embed"
+	"io/fs"
+)
+
+//go:embed all:dist
+var embedded embed.FS
+
+// Files contains the compiled Vite bundle without its dist path prefix.
+var Files = mustSub(embedded, "dist")
+
+func mustSub(source fs.FS, directory string) fs.FS {
+	files, err := fs.Sub(source, directory)
+	if err != nil {
+		panic(err)
+	}
+	return files
+}