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- subdivide (async 202, atomizing status, re-run replaces unpublished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>

web/static/css/app.css

@@ -155,6 +155,23 @@ table.list th { color: var(--muted); font-size: 0.875rem; }
 .toast.err { border-left-color: var(--err); }
 .toast.ok { border-left-color: var(--ok); }
 
+/* atomizing progress shimmer */
+.shimmer {
+  position: relative;
+  overflow: hidden;
+}
+.shimmer::after {
+  content: "";
+  position: absolute; inset: 0;
+  background: linear-gradient(90deg, transparent, color-mix(in srgb, var(--accent) 12%, transparent), transparent);
+  animation: shimmer 1.6s infinite;
+}
+@keyframes shimmer {
+  from { transform: translateX(-100%); }
+  to { transform: translateX(100%); }
+}
+input[type=range] { width: 100%; accent-color: var(--accent); }
+
 .tabs { display: flex; gap: 8px; margin-bottom: 16px; flex-wrap: wrap; }
 .tabs [aria-selected=true] { background: var(--accent); color: var(--accent-contrast); border-color: var(--accent); }