Fix duplicate migration 025 filename prefix

Renamed 025_preset_packs.sql → 030_preset_packs.sql and
030_pack_variable_extensions.sql → 031_pack_variable_extensions.sql
to match their actual version numbers (30 and 31) in lib.rs,
resolving the collision with 025_world_state_deltas.sql.

src-tauri/migrations/031_pack_variable_extensions.sql

@@ -0,0 +1,15 @@
+-- Add description and sort_order to pack variables, and custom_variable_values to stories
+
+ALTER TABLE pack_variables ADD COLUMN description TEXT;
+
+ALTER TABLE pack_variables ADD COLUMN sort_order INTEGER NOT NULL DEFAULT 0;
+
+-- Initialize sort_order based on alphabetical position within each pack
+UPDATE pack_variables SET sort_order = (
+  SELECT COUNT(*) FROM pack_variables pv2
+  WHERE pv2.pack_id = pack_variables.pack_id
+  AND pv2.variable_name < pack_variables.variable_name
+);
+
+-- Per-story custom variable value overrides (JSON object: { variableName: value })
+ALTER TABLE stories ADD COLUMN custom_variable_values TEXT;