fix: split ALTER TABLE into separate ADD COLUMN statements in migration 0002

SQLite does not support adding multiple columns in a single ALTER TABLE
statement. The previous migration tried to add 6 columns at once and
caused a syntax error, crashing the service at startup.

Bump VERSION 0.1.7 -> 0.1.8

internal/db/migrations/0002_nfs_structured.sql

@@ -1,9 +1,8 @@
-ALTER TABLE nfs_exports
-    ADD COLUMN read_only     INTEGER NOT NULL DEFAULT 0,
-    ADD COLUMN async_       INTEGER NOT NULL DEFAULT 0,
-    ADD COLUMN root_squash   INTEGER NOT NULL DEFAULT 1,
-    ADD COLUMN subtree_check INTEGER NOT NULL DEFAULT 0,
-    ADD COLUMN fsid         INTEGER NOT NULL DEFAULT 0,
-    ADD COLUMN advanced      TEXT NOT NULL DEFAULT '{}';
+ALTER TABLE nfs_exports ADD COLUMN read_only     INTEGER NOT NULL DEFAULT 0;
+ALTER TABLE nfs_exports ADD COLUMN async_        INTEGER NOT NULL DEFAULT 0;
+ALTER TABLE nfs_exports ADD COLUMN root_squash   INTEGER NOT NULL DEFAULT 1;
+ALTER TABLE nfs_exports ADD COLUMN subtree_check INTEGER NOT NULL DEFAULT 0;
+ALTER TABLE nfs_exports ADD COLUMN fsid          INTEGER NOT NULL DEFAULT 0;
+ALTER TABLE nfs_exports ADD COLUMN advanced      TEXT    NOT NULL DEFAULT '{}';
 
 CREATE INDEX IF NOT EXISTS idx_nfs_exports_fsid ON nfs_exports(fsid);