hive-agent-mcp, hive-c0re, hive-sh4re: drop agent param from get_loose_ends

get_loose_ends now always returns the caller's own loose ends, for every
caller including the manager (ruth) — there is no separate manager
surface, ruth is a normal agent with different default capabilities.

- AgentGetLooseEndsArgs removed; get_loose_ends takes no args.
- Wire Request::GetLooseEnds collapses from an Option<String> target to
  a unit variant.
- hive-c0re's handle_get_loose_ends drops the "*" hive-wide branch and
  the subtree/capability resolver (resolve_agent_state_target); both
  are gone since there is no longer a target to resolve.
- loose_ends::hive_wide and Capability::QueryAgentState removed as
  dead code — their only callers were the two functions above.
- is_descendant_of is untouched (still used by lifecycle_handlers.rs
  and schedules.rs independently of this change).
- Docs updated: docs/turn-loop/mcp.md, docs/web-ui/dashboard.md,
  docs/process/conventions.md (Loose-ends wire shape + capabilities
  table), plus the doc comments in hive-core-agent-sock, mcp_config.rs
  and capabilities.rs that described the old shape.

Refs #4480

hive-sh4re/src/permissions.rs

@@ -367,25 +367,12 @@ pub enum Capability {
     /// MCP tool `get_host_journal` is only registered in the harness
     /// when this capability is present.
     ReadHostJournal,
-    /// Agent can query agents outside its own subtree via `GetLooseEnds`,
-    /// `CountPendingReminders`, and `ReminderRollup` on the agent
-    /// socket. Without this capability, targeting an agent outside the
-    /// caller's subtree is rejected with an error (the caller itself and
-    /// every descendant are always accessible without any capability).
-    /// The `"*"` hive-wide value is not
-    /// available on the agent socket even with this capability — use the
-    /// manager socket for swarm-wide scans.
-    QueryAgentState,
 }
 
 impl Capability {
     /// Every known capability in a stable order. Use this to enumerate
     /// columns in the permissions UI or validate incoming capability strings.
-    pub const ALL: &'static [Self] = &[
-        Self::ManageRootAgent,
-        Self::ReadHostJournal,
-        Self::QueryAgentState,
-    ];
+    pub const ALL: &'static [Self] = &[Self::ManageRootAgent, Self::ReadHostJournal];
 
     /// Short human-readable description suitable for a tooltip or help text.
     #[must_use]
@@ -395,9 +382,6 @@ impl Capability {
                 "lifecycle-manage the root/manager agent on hive crash recovery"
             }
             Self::ReadHostJournal => "read host journald via get_host_journal MCP tool",
-            Self::QueryAgentState => {
-                "query non-child agents' loose ends and reminder state via get_loose_ends"
-            }
         }
     }
 }