read an agent's agents.md through the swarm and edit it with git diffs

The agent's state/AGENTS.md stays the truth and its harness the only
writer. The harness mirrors the file into a new `agents-md` KV bucket,
and swarm-controller serves that copy, so a read works while the agent is
stopped. An edit is a unified diff plus the revision it was made against,
sent over the agent's existing control subject; the harness refuses a
stale base, applies the diff with `git apply --check` then `git apply` to
a temp copy, and writes the file only when both pass. Fixes #5519.

Files:
- swarm-queue-client/src/agents_md.rs, lib.rs: the bucket name and
  subject, the mirror value, the `ApplyAgentsMd` control command and its
  reply. `AgentControl` loses `Copy` because the new variant carries text.
- hive-agent/src/swarm_agents_md.rs, main.rs: the mirror task (start,
  10 s re-read, immediate republish after an edit) and the apply.
- hive-agent/src/swarm_input.rs: the control loop answers both commands.
- hive-agent/src/claude_md_watch.rs: its AGENTS.md path is shared.
- hive-agent/Cargo.toml, Cargo.lock: sha1 for the git blob id (already in
  the lock), tempfile moves from dev to runtime for the apply directory.
- swarm-controller/src/agents_md.rs, main.rs: the bucket reader and
  GET/PUT /api/agents/{name}/agents-md; test AppState literals get the
  new field.
- swarm-controller/src/agent_control.rs: the sink hands back raw reply
  bytes, so each command decodes its own reply type.
- swarm-controller-api/src/agents_md.rs: the route bodies, shared with
  swarmctl.
- swarmctl/src/agents_md.rs, main.rs: `swarmctl agent agents-md get|apply`.
- nix/host-modules/swarm-nats.nix, nix/module-eval/nats-authelia.nix: the
  agent's publish grant on its own `$KV.agents-md.<agent>` key.

git needs no new package: agent containers enable programs.git, and the
harness unit's PATH includes /run/current-system/sw.

hive-agent/Cargo.toml

@@ -38,6 +38,8 @@ rusqlite.workspace = true
 schemars.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+# The git blob id of AGENTS.md, the revision an edit from the swarm names.
+sha1 = "0.10"
 # `agent-schedules`, `agent-inference` and `operator-profiles`: the schedule
 # ticker and the inference poller each read their own key, and the prompt
 # renderer the operator list, with one direct get.
@@ -51,6 +53,9 @@ swarm-queue-client = { workspace = true, features = [
 ] }
 # This agent's own queue secret, read from the store under its own certificate.
 swarm-secret-client.workspace = true
+# The directory an AGENTS.md edit is applied in, and the file it is written
+# through.
+tempfile = "3"
 tokio.workspace = true
 tokio-stream.workspace = true
 tower-http.workspace = true
@@ -59,7 +64,6 @@ tracing.workspace = true
 # `test-util` for `#[tokio::test(start_paused = true)]`: `swarm_agent_state`'s
 # refresh test waits out its one-minute interval on paused time.
 [dev-dependencies]
-tempfile = "3"
 tokio = { workspace = true, features = ["test-util"] }
 tower = { version = "0.5", features = ["util"] }
 # A layer that captures `swarm_queue`'s exhausted-connect log event in a test.