fix(nfs): add migration 0006 to repair fsid=0 exports

Migration 0005 (MigrateNFSClients) only runs once when first applied,
so any fsid=0 rows present before 0005 was applied never get repaired.

Migration 0006 triggers FixZeroFSIDs() which:
- Queries all nfs_exports rows with fsid=0
- Generates a new random fsid per row
- Updates the row

Version: 0.5.2

Makefile

@@ -1,5 +1,5 @@
 BINARY=nasctl
-VERSION?=0.5.1
+VERSION?=0.5.2
 GO?=go
 LDFLAGS=-s -w -X github.com/darroyo/nasctl/internal/web.Version=$(VERSION) -X github.com/darroyo/nasctl/internal/web.Commit=$(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
 BUILD_FLAGS=CGO_ENABLED=0