feat: delete task/account, edit endpoint, richer event log

- store: DeleteAccount, DeleteTask, UpdateEndpoint (+ cascade/update tests)
- httpapi: DELETE /tasks/{id}, DELETE /tasks/{id}/accounts/{accountId},
  PUT /endpoints/{id}; delete guarded with 409 while task running
- orchestrator: enrich WS events with login/host/port/error (test + run + errors)
- web: delete buttons (task, account) with confirm, endpoint edit form,
  human-readable event log (source/dest, host:port, error text)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMHQTtnQtQqL8muAXHr9kd

web/src/app.css

@@ -239,6 +239,21 @@
   color: var(--accent-strong);
 }
 
+.link-btn.danger {
+  color: var(--fg-faint);
+  border-bottom-color: transparent;
+}
+
+.link-btn.danger:hover {
+  color: var(--danger, #ff5c5c);
+  border-bottom-color: var(--danger, #ff5c5c);
+}
+
+.link-btn:disabled {
+  opacity: 0.4;
+  cursor: not-allowed;
+}
+
 /* ---------- buttons ---------- */
 
 .btn {