fix(admin): keyset export paging, rollup-free spend, consistent totals

Review pass over the preceding commits.

- The activity export paged by OFFSET. The journals are append-only and the
  feed is newest-first, so rows written mid-export shift the window down and
  repeat rows already emitted. Pages by keyset on (created_at, feed, id) now.
- top_token_users and the per-user breakdown counted run-level rollup rows.
  A scheduled run already has a row per LLM call, so its spend was billed
  twice -- invisible while the column was tokens, obvious once it was dollars.
  Both now exclude them, matching every other spend query.
- total_cost was summed from the per-model split, which drops rows with no
  model_id and so undercounted the figure printed above the series. Summed
  from the series instead.
- The CSV export encoded its detail cell without the fallback the NDJSON
  branch had, so a non-JSON-native value would have failed the stream.
- The activity view reset pagination in an effect, which fetched the stale
  page against the new filters before fetching again. Reset in the setters.
- The audit taxonomy is no longer re-exported from the helper module; the one
  caller that wanted it imports from where it lives.

docsgpt/api/user/sources/upload.py

@@ -397,10 +397,6 @@ class UploadFile(Resource):
             return make_response(jsonify({"success": False}), 400)
         # Predetermined id matches the dedup-claim row; loser GET sees same.
         response_task_id = predetermined_task_id or task.id
-        # ``source_uuid`` was minted above and passed to the worker as
-        # ``source_id``; the worker uses it verbatim for every SSE event,
-        # so the frontend can correlate inbound ``source.ingest.*`` to
-        # this upload regardless of whether an idempotency key was set.
         # Audited here, not in the worker: this is the user action. The
         # ingest may still fail, which the source's own status records.
         try:
@@ -416,9 +412,15 @@ class UploadFile(Resource):
                 )
         except Exception as err:
             current_app.logger.warning(
-                "Could not audit upload for source %s: %s", source_uuid, err,
+                "Could not audit upload for source %s: %s",
+                source_uuid,
+                err,
                 exc_info=True,
             )
+        # ``source_uuid`` was minted above and passed to the worker as
+        # ``source_id``; the worker uses it verbatim for every SSE event,
+        # so the frontend can correlate inbound ``source.ingest.*`` to
+        # this upload regardless of whether an idempotency key was set.
         response_payload: dict = {
             "success": True,
             "task_id": response_task_id,