feat: metrics dashboards with SVG charts, CSV export, leaderboard (phase 10)

- aggregations over the immutable bountyAwards ledger: totals, weekly
  buckets ($dateTrunc), per-developer and per-customer groupings
- timeline-derived: approval rate, time logged, assigned→approved lead
  time, imported→published atomization lead time, open board depth
- developer + consultant dashboards (admin = global consultant view),
  date-range filters, CSV export of the ledger
- leaderboard (top 10 by bounty) honoring the new leaderboardOptOut
  profile setting
- hand-rolled SVG line and bar charts (~150 lines, no chart library)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/http/server.go

@@ -88,6 +88,7 @@ func New(cfg *config.Config, log *slog.Logger, reg *metrics.Registry, st *store.
 	s.routesConsultant(mux)
 	s.routesWorkResults(mux)
 	s.routesMessages(mux)
+	s.routesMetrics(mux)
 	mux.HandleFunc("GET /ws", s.handleWS)
 	s.routesWeb(mux)