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

docs/process/conventions.md

@@ -181,14 +181,12 @@ privileged bot, etc.) can land later without breaking existing
 handlers. Each row carries enough context that the caller renders
 it directly as a bulleted list, no follow-up fetch needed.
 
-Per-flavour scoping is uniform across the two cancellable variants:
-
-- **agent-flavour** `GetLooseEnds` only surfaces rows the calling
-  agent has standing in. `Approval` rows only appear when the
-  calling agent is the manager (sub-agents don't submit
-  approvals). `Reminder` rows are scoped to `owner == self`.
-- **manager-flavour** `GetLooseEnds` lists every pending row in
-  the swarm — full audit view.
+`GetLooseEnds` takes no target — it always returns the caller's own
+rows, on both the agent and manager sockets alike (the manager, `ruth`,
+is a normal agent here, just auto-deployed with different default
+capabilities). `Approval` rows only appear when the calling agent is
+the manager (sub-agents don't submit approvals). `Reminder` rows are
+scoped to `owner == self`.
 
 Per-variant fields:
 
@@ -364,7 +362,6 @@ that allows the underlying resource access.
 |---|---|
 | `manage_root_agent` | may lifecycle-manage the root/manager agent via `kill`/`start`/`restart` |
 | `read_host_journal` | registers the `get_host_journal` MCP tool + serves `GET /journal-host` requests |
-| `query_agent_state` | may call `get_loose_ends` / `CountPendingReminders` targeting non-child agents |
 
 **Config storage** — per-agent capabilities live in
 `/var/lib/hyperhive/meta/capabilities.json` alongside `tool-groups.json`.