Partition files by age (id)

New rows went into free space scattered through the 9.6 GB heap on the HDD
(left behind by inspection's updates): one random HDD read per insert, and
seed batches took a median 13 s to store. The existing table becomes the
first partition as it is (a CHECK scan, no rewrite; indexes, its foreign
key and the triggers are taken over by the partitioned parent); new
partitions of 4M ids go in the same tablespace and stay in memory while
they fill.

- Every partition has a unique file_key index; FileStore.insert looks keys
  up in all partitions first (a key can't be unique across partitions).
- FilePartitions.ensure() (gc:scheduler) keeps two partitions ahead.
- Stats count files from the partitions; seed:node waits ~20 minutes for
  the API before giving a range up.

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

app/services/SearchService.ts

@@ -390,7 +390,8 @@ class SearchService {
         SELECT r.name, r.size, r.file_count, r.encrypted, coalesce(r.source, 'unknown') AS source
         FROM releases r TABLESAMPLE SYSTEM (0.5) WHERE ${VISIBLE_SQL})
       SELECT (SELECT reltuples FROM pg_class WHERE relname = 'releases_category_idx') AS releases,
-             (SELECT reltuples FROM pg_class WHERE relname = 'files') AS files,
+             -- files is partitioned (D39): its partitions hold the counts.
+             (SELECT sum(c.reltuples) FROM pg_inherits i JOIN pg_class c ON c.oid = i.inhrelid WHERE i.inhparent = 'files'::regclass) AS files,
              (SELECT count(*) FROM sample) AS sampled,
              (SELECT count(*) FROM sample WHERE is_readable_name(name)) AS sampled_readable,
              -- Indexed data only: a spot listing's size is what the spot announces.