feat: atomization pipeline with job queue, atomizer client, WS hub, and board UI (phase 7)

- internal/extsvc: circuit breaker (§11.16) + retrying bearer JSON client
- atomizer client: §5.1 contract incl. defensive coefficient normalization
  and extension coefficient range (0,2]
- persisted jobs collection: atomic claim, panic recovery, exponential
  backoff (max 3), stale-running requeue, shutdown-safe bookkeeping
- subdivide (async 202, atomizing status, re-run replaces unpublished
  children after confirm) and extend (sibling task, source budget)
- failure path reverts status and notifies the consultant on final attempt
- PATCH task editing with bounty recompute, budget cascade to descendants
- publish single + bulk; task detail endpoint role-scoped
- coder/websocket hub: multiplexed channels, origin check, 30s heartbeats;
  client ws.js with reconnect + 15s polling fallback
- consultant atomization board: tree by root, coefficient sliders with live
  per-parent sum indicator, bounty preview, modals, shimmer, atomizer-down
  gating via /api/v1/service-health
- fix: tasks external-ref unique index is partial, not sparse (compound
  sparse indexed every task through customerId and broke child inserts)

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

internal/http/server.go

@@ -39,6 +39,8 @@ type Server struct {
 	jobsProvider StatusProvider
 	syncTrigger  func(customerID string)
 	publishFn    func(channel, event string, payload any)
+	enqueueFn    func(ctx context.Context, kind string, payload any) (string, error)
+	wsHandler    func(w http.ResponseWriter, r *http.Request, userID string)
 }
 
 func New(cfg *config.Config, log *slog.Logger, reg *metrics.Registry, st *store.Store, fs *files.Store) *Server {
@@ -67,6 +69,8 @@ func New(cfg *config.Config, log *slog.Logger, reg *metrics.Registry, st *store.
 	s.routesAuth(mux)
 	s.routesProfile(mux)
 	s.routesAdmin(mux)
+	s.routesTasks(mux)
+	mux.HandleFunc("GET /ws", s.handleWS)
 	s.routesWeb(mux)
 
 	s.httpSrv = &http.Server{