fix(pricing): book daily cost to the day tokens were spent

token_usage holds a session's cumulative totals with no time, so
/api/pricing/cost booked a multi-day session's whole cost to its start
date and the status bar's Today read ~$0. TranscriptCache now also splits
usage by each message's UTC hour (tokensByHour); the hook writer stores it
in the new token_usage_hourly table (MAX per hour) and the server
back-fills existing sessions at start. The daily split books each total
over its hourly rows' local days and the rest to the start date, so the
days still add up to the total.

server/routes/settings.js

@@ -143,6 +143,7 @@ router.post("/clear-data", (_req, res) => {
   const counts = getTableCounts();
   db.pragma("foreign_keys = OFF");
   db.prepare("DELETE FROM token_usage").run();
+  db.prepare("DELETE FROM token_usage_hourly").run();
   db.prepare("DELETE FROM events").run();
   db.prepare("DELETE FROM agents").run();
   db.prepare("DELETE FROM sessions").run();
@@ -368,6 +369,9 @@ router.post("/cleanup", (req, res) => {
         .prepare(`DELETE FROM agents WHERE session_id IN (${placeholders})`)
         .run(...ids).changes;
       db.prepare(`DELETE FROM token_usage WHERE session_id IN (${placeholders})`).run(...ids);
+      db.prepare(`DELETE FROM token_usage_hourly WHERE session_id IN (${placeholders})`).run(
+        ...ids
+      );
       db.prepare(`DELETE FROM sessions WHERE id IN (${placeholders})`).run(...ids);
       result.purged_sessions = toDelete.length;
     }