refactor(db): split revision preview from meta_json

Preview BIRD-фрагменты в config_revision_preview; meta_json только счётчик префиксов.

Co-authored-by: Cursor <[email protected]>

migrations/sqlite/000015_revision_preview.up.sql

@@ -0,0 +1,13 @@
+CREATE TABLE config_revision_preview (
+    revision_id   TEXT NOT NULL PRIMARY KEY REFERENCES config_revision (id) ON DELETE CASCADE,
+    fragments     TEXT NOT NULL DEFAULT '{}'
+);
+
+INSERT INTO config_revision_preview (revision_id, fragments)
+SELECT id, json(COALESCE(json_extract(meta_json, '$.preview_fragments'), '{}'))
+FROM config_revision
+WHERE json_extract(meta_json, '$.preview_fragments') IS NOT NULL;
+
+UPDATE config_revision
+SET meta_json = json_remove(meta_json, '$.preview_fragments')
+WHERE json_extract(meta_json, '$.preview_fragments') IS NOT NULL;