v0.6.0 — Backup & Restore page; install netcat for Postgres-wait

Version the backup/restore feature that merged in unversioned, and add
netcat-openbsd to the bookworm-slim runtime so the new entrypoint Postgres
readiness check (nc -z postgres 5432) works instead of looping forever.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/version.ts

@@ -1,2 +1,2 @@
 // Bump on every user-visible release. Changelog entries live in `src/lib/changelog.ts`.
-export const APP_VERSION = "0.5.2";
+export const APP_VERSION = "0.6.0";