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/tools/README.md

@@ -44,4 +44,4 @@ debug agent behavior.
   (`mcp__matrix__*`) for agents with a matrix account, multiple
   accounts per agent, and declaring extra MCP servers generally.
 - **[scheduling](scheduling.md)** — scheduled prompts (operator
-  approval required) and the `get_host_journal` diagnostics tool.
+  approval required).

docs/tools/scheduling.md

@@ -66,31 +66,6 @@ body, per-target `last_fired_at` and `last_result`,
 `next_fire_at_unix`, `interval_seconds`. Use to look up an id before
 cancelling, or to audit upcoming wake-ups across the hive.
 
-## `read_host_journal` capability
-
-Capability-gated (not a tool group) — the operator enables it in the
-P3RM1SS10NS C4P4B1L1T13S section. Unlike tool groups this isn't
-configurable from `agent.nix`.
-
-### `get_host_journal(unit?, container?, lines?, priority?, grep?, since?, until?)`
-
-Fetch recent lines from the **host** journal (requires
-`read_host_journal` capability). Useful when you need visibility
-outside your own container — infrastructure services, hive-c0re
-lifecycle events, or another container's boot log.
-
-- `unit` — filter to a systemd unit (for example `hive-c0re.service`).
-- `container` — nspawn machine name verbatim. Agent containers use
-  the `h-<name>` prefix (for example `h-iris`); infrastructure containers
-  use their full name (for example `hive-ci`, `hive-forge`, `hive-matrix`).
-  Omit for the host journal. The gateway has no machine — its nginx
-  runs on the host, so read it with `unit: nginx.service` and no
-  `container`.
-- `lines` — how many lines to return (default 30, max 100).
-- `priority` — minimum syslog level (`emerg` … `debug`).
-- `grep` — regex matched against log message fields (`journalctl --grep`).
-- `since` / `until` — time bounds (for example `-1h`, `2024-01-01 12:00:00`).
-
 ## See also
 
 - `remind` (no-approval self-wake path) — documented in