refactor(sync): move the delta feed's domain pages out of its route

src/__tests__/baselines/version-stamp-comments.json

@@ -1,7 +1,7 @@
 {
   "$comment": "Comment lines that open with a release version, per file under src/. Maintained by src/__tests__/version-stamp-ratchet.test.ts.",
-  "count": 2915,
-  "total": 9853,
+  "count": 2914,
+  "total": 9848,
   "entries": {
     "__tests__/account-payload-consumer-guard.test.ts": 2,
     "__tests__/acting-account-boundary-guard.test.ts": 7,
@@ -533,7 +533,6 @@
     "app/api/strava/credentials/route.ts": 1,
     "app/api/strava/disconnect/route.ts": 1,
     "app/api/strava/status/route.ts": 1,
-    "app/api/sync/changes/route.ts": 5,
     "app/api/sync/state/route.ts": 2,
     "app/api/telegram/webhook/__tests__/route.test.ts": 3,
     "app/api/user/ai-provider/__tests__/legacy-private-host.test.ts": 1,