remove the get_host_journal MCP tool and its capability

swarm-logs covers every host-tier unit this tool could reach, so the
second, capability-gated path into host journald earns nothing and is
removed outright rather than disabled behind a flag.

Removed end to end: the MCP tool definition + handler, the
GetHostJournal/HostJournal wire variants, hive-c0re's
dispatch_host_journal handler, the ReadHostJournal capability, and the
harness-side capability->--allowedTools gate. get_host_journal was the
only capability that mapped to an MCP tool, so allowed_capability_tools
could only ever return an empty vec; it goes too rather than linger as a
function that provably does nothing.

capabilities::has_cap/caps_for stay: #4624 gave ManageRootAgent's
bind-mount enforcement (hive-c0re/src/lifecycle/host_config.rs) a
second caller of has_cap, so they're no longer callerless once this
lands on top of it.

hive-sh4re's journal module (JournalPriority) had no consumer outside
this tool and is deleted.

An existing capabilities.json still naming read_host_journal does not
error: capabilities::prune_unknown drops unrecognised names with a
warn!, and an agent left with no capabilities has its entry removed. No
migration step is needed.

Untouched: hive-c0re/src/dashboard/journal.rs's
read_host_journal_response, which matches the name but is the private
helper behind the operator-only GET /api/journal-host dashboard route
and carries no capability check.

docs/turn-loop/mcp.md

@@ -150,11 +150,10 @@ hive_name?, swarm_name?, matrix_accounts? }`. `matrix_accounts` is a
   and `WebSearch` tools (not MCP tools; added directly to the
   `--allowedTools` list). Off by default; add the group in the
   P3RM1SS10NS tab and rebuild to enable.
-- **Capability-gated** — `get_host_journal` (requires
-  `read_host_journal` capability set via the P3RM1SS10NS tab;
-  orthogonal to tool groups). Full list of capabilities and their
-  effects in [`docs/process/conventions.md#capabilities`](../process/conventions.md).
-  Also documented in [`docs/tools/scheduling.md`](../tools/scheduling.md).
+- **Capabilities** — orthogonal to tool groups, set via the P3RM1SS10NS
+  tab. No capability registers an MCP tool today; the full list and their
+  effects are in
+  [`docs/process/conventions.md#capabilities`](../process/conventions.md).
 - **Matrix MCP + extra servers** — `mcp__matrix__*` tools and
   per-agent extra MCP config. See
   [`docs/tools/matrix.md`](../tools/matrix.md).