grant manage_root_agent by stored permission only, not by the name ruth

Permission::default_for and hive-sh4re's MANAGER_AGENT are gone: every
agent with no permissions key holds Permission::DEFAULT, ruth included.
The agent-name parameters that only fed default_for go with it
(permissions::effective, HiveCopy::before_read/after_read and their
callers).

swarm-controller seeds the grant ruth held by name: at start, a declared
ruth whose permissions are unset gets DEFAULT plus manage_root_agent
written into her key, once, logged. A set key is never touched. It is a
one-shot to delete once every swarm has passed it.

The swarm UI setup assistant opens the create form with
manage_root_agent checked, so a new ruth is created with the grant.
permissions_import no longer adds ruth to the import or splits her
default. Docs and help text no longer say ruth holds the grant by
default; swarmctl-cli.md regenerated.

swarmctl/src/main.rs

@@ -296,8 +296,7 @@ enum AgentVerb {
     /// The agent applies its tool permissions at its next turn; the hive
     /// running it restarts it, after its current turn, when
     /// `manage_root_agent` changes. Unset leaves the agent on the default:
-    /// `messaging`, `meta`, `inbox`, `execution`, plus `manage_root_agent`
-    /// for `ruth`.
+    /// `messaging`, `meta`, `inbox`, `execution`, whatever its name.
     Permissions {
         #[command(subcommand)]
         command: PermissionsVerb,