feat(stats): voice-time and message leaderboards per space

Voice stays get their own table rather than joining the audit log: that table
records points in time, a call is an interval, and pairing join/leave point
events would leave every query guessing at joins whose leave never arrived.

Sessions are opened and closed inside joinRoom/leaveCurrentRoom rather than at
the seven call sites that reach them, so no path can be missed, and
destroyRoom closes them too — it bypasses leaveCurrentRoom and would otherwise
leak open rows.

A restart leaves sessions open with an unknowable end time. They are closed at
startedAt, discarding that time rather than inventing it: crediting the gap
would hand someone hours they never spent, and the numbers are the point.
Mirrors the existing users.status sweep on boot.

Only closed sessions count, so a figure does not move on every refresh. Bars
scale to the leader, not the total — with five people every share of a total
looks identical. Statistics are readable by any member, since they are the
group's own numbers; the audit log, which names who did what, stays on
MANAGE_SPACE.

packages/web/src/i18n/locales/en.ts

@@ -33,6 +33,20 @@ export const en = {
   'settings.voice.micTest.idle': 'Test your mic without joining a call.',
   'settings.voice.micTest.failed': 'Could not open the microphone. Check the device and its permission.',
 
+  // Statistics
+  'stats.title': 'Statistics',
+  'stats.range.7': 'Last 7 days',
+  'stats.range.30': 'Last 30 days',
+  'stats.range.365': 'Last year',
+  'stats.voice.title': 'Time in voice',
+  'stats.messages.title': 'Messages sent',
+  'stats.empty': 'Nothing recorded in this period yet.',
+  'stats.total.voice': '{value} total',
+  'stats.total.messages': '{value} messages in total',
+  'stats.hours': '{hours}h {minutes}m',
+  'stats.minutes': '{minutes}m',
+  'stats.note': 'Counting started when this feature was installed — earlier activity is not included.',
+
   // Audit log
   'audit.title': 'Audit Log',
   'audit.empty': 'Nothing recorded yet. Changes to the server show up here.',