agents get a todo when assigned to an issue or PR, rewritten when unassigned and cleared on close

A new swarm service, swarm-notify-router, in its own container on the host
that sets deploy.notify-router.enable (defaulted on by allSwarmServices where
the host has the router's store leaf, like the claude login minter).

- swarm-controller registers instance-wide hooks for `issues` +
  `issue_assign` and `pull_request` + `pull_request_assign`, updates the
  event list of a hook already registered with fewer (leaving its active flag as it is), and keeps each
  verified body unchanged in the SWARM_EVENTS stream on
  $SWARM.events.forge.<X-Forgejo-Event-Type>, deduped by X-Forgejo-Delivery.
  A delivery the stream did not keep answers 503.
- swarm-notify-router drains its durable consumer on that stream, runs its
  flows (source -> match -> todo sink, stored as nodes plus edges and checked
  to be a tree) and queues each op on $SWARM.router.todo.<agent> in the
  work-queue stream ROUTER_TODOS. Built-in flows: assigned, unassigned (same
  key, rewritten) and closed (prefix-clears every holder's router todos). A
  per-issue snapshot in its notify-router-state bucket holds the last
  assignees and the todo holders; only agents in the agent-status bucket get
  ops, and an assignee that was not one is left out of the snapshot so the
  next assign event retries it. After the first event that must be retried,
  the rest of the batch is nakked so redelivery keeps stream order.
- hive-agent creates its own durable consumer todo-<agent> and applies each
  op to its todo store as subsystem `router`, then acks; a refused op stops
  the rest of its batch the same way. The store's (subsystem, key) dedup
  makes a redelivery harmless. New Todos::clear_prefix.
- swarm-nats-auth: a --notify-router-client arm; the controller may publish
  $SWARM.events.forge.*; each agent gets three {agent} templates (extended
  consumer create whose filter the server checks, MSG.NEXT, ACK).
- Credentials: a notify-router store leaf minted by glue-bao-tls, a
  swarm-notify-router bao policy (read on its own queue client secret), an
  authelia machine client, the secret publisher entry, a journal forwarder
  route. No manual step.

hive-forge-notify is unchanged, so agents also still get forge's own
notifications.

Refs #5571

docs/swarm/secrets.md

@@ -412,7 +412,7 @@ next controller restart.
 ### Per-principal identities
 
 Bao matches a cert-auth role on the certificate's subject, so a certificate is an
-identity and sharing one merges the identities. Each of these ten leaves has
+identity and sharing one merges the identities. Each of these eleven leaves has
 a role and a policy of its own, and reaches one path, except the review
 classifier's, the CI runner's, the builder's, the CI run poller's, the claude
 login minter's, the forge host's and Grafana's, which reach more than one:
@@ -426,6 +426,7 @@ login minter's, the forge host's and Grafana's, which reach more than one:
 | `swarm-bao-ci-runner`, and the runner's journal forwarder in its container                              | `ciRunnerClientCertFile` / `ciRunnerClientKeyFile`                 | `swarm/services/ci-runner/registration-token` and `swarm/services/<runner forwarder client id>/oidc/client`                                                                                  |
 | `swarm-review-classifier`, in its container                                                             | `reviewClassifierClientCertFile` / `reviewClassifierClientKeyFile` | `swarm/services/review-classifier/anthropic-api-key`, `swarm/services/review-classifier/acp-provider` and `swarm/services/<classifier client id>/oidc/client`                                |
 | `swarm-claude-login`, in its container                                                                  | `claudeLoginClientCertFile` / `claudeLoginClientKeyFile`           | creates and updates `swarm/agents/+/claude-credentials`; reads `swarm/services/<minter client id>/oidc/client`                                                                               |
+| `swarm-notify-router`, in its container                                                                 | `notifyRouterClientCertFile` / `notifyRouterClientKeyFile`         | `swarm/services/<router client id>/oidc/client`                                                                                                                                              |
 | `swarm-builder`, in its container                                                                       | `builderClientCertFile` / `builderClientKeyFile`                   | `swarm/services/builder/forge/token` and `swarm/services/<builder client id>/oidc/client`                                                                                                    |
 | `swarm-ci-metrics`                                                                                      | `ciMetricsClientCertFile` / `ciMetricsClientKeyFile`               | `swarm/services/ci-metrics/forge/token` and `swarm/services/<poller client id>/oidc/client`                                                                                                  |
 | `swarm-bao-forge-oidc` and the forge's controller-token mint and its journal forwarder in its container | `forgePublisherClientCertFile` / `forgePublisherClientKeyFile`     | writes `swarm/controller/swarm-controller/forge/token`; reads `swarm/services/<forge client id>/oidc/client` and `swarm/services/<forge forwarder client id>/oidc/client`                    |