Stats: range buttons follow the retention settings

The Statistics page offers only the ranges kept (longest of the minute,
hour and day retentions), adds 1y and 2y when the daily data covers them,
caps the heatmap at the hourly retention and links to Explore within
retention.queries. Status and explore send retention_seconds. The query
log error names stats.retention.queries.

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

internal/stats/store.go

@@ -45,7 +45,7 @@ var schema = []string{
 		PRIMARY KEY (res, ts, kind, key)
 	) WITHOUT ROWID;
 	CREATE TABLE meta (key TEXT PRIMARY KEY, value TEXT NOT NULL);`,
-	// 2: the query log, every answer for a while (stats.query_retention),
+	// 2: the query log, every answer for a while (stats.retention.queries),
 	// for drilling down: what a client asked, who asked for a name
 	// (docs/stats.md#exploring).
 	`CREATE TABLE queries (