swarm UI: log an agent into claude from its card; the credentials go to bao and the agent picks them up

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

- swarm-ui: an agent card showing "login needed" gets a "log in" button.
  Its dialog starts the login, shows the URL claude printed, and takes the
  pasted code.
- swarm-controller: `POST/DELETE /api/agents/{name}/claude-login` and
  `POST /api/agents/{name}/claude-login/code`, behind the swarm UI's
  authelia-gated `/api/`, relay the steps to the minter as requests on
  `$SWARM.claude-login.request`.
- swarm-claude-login: runs `claude auth login` over piped stdio with HOME
  and CLAUDE_CONFIG_DIR in a per-login scratch dir, scrapes the first
  https URL, writes the code to stdin, and stores the `.credentials.json`
  at `swarm/agents/<agent>/claude-credentials` with a KV v2 write, a new
  version over any earlier one. The scratch dir goes on every exit path; a
  login waits 15 minutes for its code.
- hive-agent: while parked in `wait_for_login`, reads that leaf every 30 s
  under the agent's own cert and installs it only when its KV version is
  newer than the one recorded in `<harness>/claude-credentials-version`.
  An equal or older version is never put back, because claude rotates the
  refresh token and the stored copy is stale after the first refresh.
- swarm-secret-client: `claude_login` paths and `SecretStore::read_versioned`.
- Credentials: a `claude-login` store leaf minted by glue-bao-tls, a
  `swarm-claude-login` policy (create/update on
  `swarm/agents/+/claude-credentials`, read on its own queue client
  secret), an authelia machine client, and a `--claude-login-client`
  grant in the queue's auth-callout responder. The unit runs as a static
  system user.

The hive's own web-UI login is unchanged.

Refs #5268

nix/host-modules/swarm-bao.nix

@@ -1054,6 +1054,22 @@ let
     }
   ];
 
+  # The claude login minter: every agent's `claude-credentials` leaf,
+  # create and update so a relogin replaces the last, and nothing else under
+  # an agent; and its own queue client secret, read at start.
+  claudeLoginWriters = [
+    {
+      name = "swarm-claude-login";
+      cn = baoDeploy.claudeLoginCommonName;
+      policyText = ''
+        path "${credentialMountPath}/data/swarm/agents/+/claude-credentials" {
+          capabilities = ["create", "update"]
+        }
+      ''
+      + readStanza "${credentialMountPath}/data/swarm/services/${hyperhiveCfg.swarm.claude-login.clientId}/oidc/client";
+    }
+  ];
+
   # The forge host's one store identity. `swarm-bao-forge-publisher` writes
   # the controller's forge token under it, the one writer of that path and
   # write-only: it copies a file in and never reads one back.
@@ -1932,6 +1948,19 @@ in
       '';
     };
 
+    claudeLoginCommonName = lib.mkOption {
+      type = lib.types.str;
+      default = "swarm-claude-login";
+      description = ''
+        Subject the store's `swarm-claude-login` cert-auth role accepts: the
+        identity the claude login minter presents from inside its container.
+        Its grant is create and update on `swarm/agents/+/claude-credentials`
+        and read on its own queue client secret.
+
+        ⚠️ Reserved as a hive name by ./swarm.nix, like its siblings.
+      '';
+    };
+
     forgePublisherCommonName = lib.mkOption {
       type = lib.types.str;
       default = "swarm-forge-publisher";
@@ -2232,6 +2261,31 @@ in
       '';
     };
 
+    claudeLoginClientCertFile = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = "/var/lib/swarm-bao-pki/claude-login.pem";
+      description = ''
+        Certificate the claude login minter presents to the store. Its subject
+        must be {option}`services.hyperhive.deploy.bao.claudeLoginCommonName`.
+
+        ./glue-bao-tls.nix points it at the leaf it mints on the store's host.
+        On a minter host without the store, it is a file the operator copies
+        from the store's host. A path, never a value.
+      '';
+    };
+
+    claudeLoginClientKeyFile = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = "/var/lib/swarm-bao-pki/claude-login-key.pem";
+      description = ''
+        Private key for
+        {option}`services.hyperhive.deploy.bao.claudeLoginClientCertFile`.
+        A path, never a value.
+      '';
+    };
+
     forgePublisherClientCertFile = lib.mkOption {
       type = lib.types.nullOr lib.types.str;
       default = null;
@@ -3318,6 +3372,8 @@ in
 
       systemd.services.swarm-bao-builder-policy = readerPolicyUnit "write the swarm builder's forge-token-reader bao policy and cert-auth role" builderReaders;
 
+      systemd.services.swarm-bao-claude-login-policy = readerPolicyUnit "write the claude login minter's credentials-writer bao policy and cert-auth role" claudeLoginWriters;
+
       systemd.services.swarm-bao-forge-publisher-policy = readerPolicyUnit "write the forge's controller-token-publisher bao policy and cert-auth role" forgePublisherWriters;
 
       # A FOURTH sibling, same shape and same reasons as the two above. This