Scalability: journal:index is read/rewritten in full on every append and every list

src/kv.ts appendJournalEntry reads the whole journal:index array, pushes one id, writes the whole array back on every single append. listJournalEntries reads journal:index then fetches every entry with kv.get in a Promise.all, then filters by since/limit in memory - no pagination against KV itself.

As the journal grows this is O(n) KV read+write per append and O(n) KV reads per list call. Since there is no promotion-driven pruning of old entries visible in scripts/promote.ts (it never deletes, only tracks review state locally), journal:index will grow unbounded over the life of the deployment.

Worth deciding: either (a) archive/prune promoted entries out of journal:index via a script, or (b) switch listing to KV list-by-prefix with cursor pagination instead of an index array, or (c) explicitly document a expected max journal size and revisit before it is exceeded.