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

nix/host-modules/swarm-nats.nix

@@ -867,6 +867,9 @@ in
                 "--builder-client ${lib.escapeShellArg config.services.hyperhive.swarm.builder.clientId}"
                 # Hears login steps and answers each by reply, and nothing else.
                 "--claude-login-client ${lib.escapeShellArg config.services.hyperhive.swarm.claude-login.clientId}"
+                # Drains its consumer on the forge events stream and queues
+                # agents' todo ops (`swarm-nats-auth`'s `notify_router_permissions`).
+                "--notify-router-client ${lib.escapeShellArg config.services.hyperhive.swarm.notify-router.clientId}"
                 # What an agent may publish to, keyed on its own name: its
                 # terminal rows and its turn-state header
                 # (`hive-agent::swarm_agent_state`), two subject families so a
@@ -914,6 +917,16 @@ in
                 # (`swarm_queue_client::agents_md_initial`), on the same terms: the
                 # harness reads the text its `AGENTS.md` starts with.
                 "--agent-token-publish-subject ${lib.escapeShellArg "\$\$JS.API.DIRECT.GET.KV_agents-md-initial.\$\$KV.agents-md-initial.{agent}"}"
+                # Its own durable consumer on the notification router's
+                # `ROUTER_TODOS` stream (`swarm_wire::router_todo`): create it
+                # in the extended form whose last tokens are the filter, which
+                # the server checks against the payload, so the consumer
+                # delivers this agent's subject alone; pull from it; ack what
+                # it delivered. No bare `CONSUMER.CREATE`, no `STREAM.INFO`
+                # and no publish on the subjects: the router is their writer.
+                "--agent-token-publish-subject ${lib.escapeShellArg "\$\$JS.API.CONSUMER.CREATE.ROUTER_TODOS.todo-{agent}.\$\$SWARM.router.todo.{agent}"}"
+                "--agent-token-publish-subject ${lib.escapeShellArg "\$\$JS.API.CONSUMER.MSG.NEXT.ROUTER_TODOS.todo-{agent}"}"
+                "--agent-token-publish-subject ${lib.escapeShellArg "\$\$JS.ACK.ROUTER_TODOS.todo-{agent}.>"}"
                 # Every agent also reads the operator list, the one key of the
                 # `operator-profiles` bucket, with one direct get. That grant
                 # names no agent, so the responder adds it itself