reminders: add ListReminders IPC + /reminders web page

Store layer: ListReminders returns the n most recent reminders
(newest first). IPC: new MethodListReminders wired through server,
client, and lockedAPI. Web: /reminders page with table of created
time, fire time, status badge, and payload text; empty state with
prompt to ask maven for a reminder. Sidebar entry under Automation.

cmd/mavend/main.go

@@ -109,6 +109,7 @@ func (l *lockedAPI) Since(ctx context.Context, key string, now time.Time) (time.
 func (l *lockedAPI) Presence(ctx context.Context) (ipc.Presence, error)                 { return ipc.Presence{}, errLocked }
 func (l *lockedAPI) CreateReminder(ctx context.Context, fire time.Time, payload, cron string) (int64, error) { return 0, errLocked }
 func (l *lockedAPI) MarkReminder(ctx context.Context, id int64, status string) error              { return errLocked }
+func (l *lockedAPI) ListReminders(ctx context.Context, n int) ([]ipc.Reminder, error)             { return nil, errLocked }
 func (l *lockedAPI) RecordNudge(ctx context.Context, rule, channel, message string, ts time.Time) (int64, error) { return 0, errLocked }
 func (l *lockedAPI) ResolveNudge(ctx context.Context, id int64, outcome string, ts time.Time) error               { return errLocked }
 func (l *lockedAPI) RecentOutcomes(ctx context.Context, rule string, n int) ([]string, error)         { return nil, errLocked }