Statistics page: the statistics database's size, and a fullness bar on the disk tiles

The server section shows the statistics database's size (with its -wal and -shm) and how many answers the query log holds, linking to the dashboard's Storage panel; the disk tiles get the same bar as the dashboard. GET /stats/server has database {path, bytes, query_log_rows}.

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

docs/stats.md

@@ -221,8 +221,10 @@ view switches apply here too.
 `anonymize_clients` and `exclude_clients` apply to the query log as to
 everything else. Its size: each answer takes about 150 to 200 bytes with
 its indexes, so 50,000 answers a day for 7 days is about 60 MB, 200,000 a
-day about 250 MB. The dashboard's Storage panel shows the databases' size
-and how many answers the query log holds.
+day about 250 MB. The Statistics page's server section shows the
+statistics database's size and how many answers the query log holds, next
+to the disks (with a bar of how full each is); the dashboard's Storage
+panel has all of Jarl's databases.
 
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