fix(server): stop the background compaction before the database is closed

The compaction starts right away in NewServer and could still write to the SQLite files while a
test's temp dir was removed ("directory not empty" on the CI runner, TestWebhookTokenInURLOnlyAPIKey).
Server.Close stops it and waits for a running pass; tests call it before closing the store, and the
server calls it on shutdown before the deferred store.Close. v0.37.1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "mindsift-frontend",
-  "version": "0.37.0",
+  "version": "0.37.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "mindsift-frontend",
-      "version": "0.37.0",
+      "version": "0.37.1",
       "license": "Unlicense",
       "dependencies": {
         "@fontsource-variable/inter": "5.3.0",