docs: persistence and config changes become one operator page

The operator parts of the persistence and config-changes pages merge into
agents/persistence.md. The sqlite tables, state dirs, mounts and migrations move
to 4-implementation/agent-state/persistence.md, and the deploy path, meta flake,
deploy markers, startup migrations, root container, system messages and
autoupdate move to 4-implementation/agent-state/config-changes.md. Links, code
comments and nix comments that named the old sections point at the new pages.

hive-c0re/src/lifecycle/host_config.rs

@@ -289,7 +289,7 @@ async fn systemd_daemon_reload() -> Result<()> {
 }
 
 /// Append the bind flag for `child`'s `state` dir into `binds`. See
-/// docs/2-handbook/agents/persistence.md ("Cross-agent access to state") for what
+/// docs/4-implementation/agent-state/persistence.md ("Cross-agent access to state") for what
 /// the holder may touch and why. Creates the missing host-side directory so
 /// nspawn doesn't refuse to start; a missing dir is non-fatal.
 ///

hive-c0re/src/migrate.rs

@@ -17,7 +17,7 @@
 //!   `agent-permissions` bucket when the swarm UI creates her.
 //!
 //! Kill-switch: `HIVE_SKIP_META_MIGRATION=1`. Full sequence and phase
-//! details: `docs/2-handbook/agents/config-changes.md::Startup migrations (older hosts)`.
+//! details: `docs/4-implementation/agent-state/config-changes.md::Startup migrations (older hosts)`.
 
 use std::path::Path;
 use std::time::Duration;

hive-c0re/src/stores/build_logs.rs

@@ -1,7 +1,7 @@
 //! Sqlite-backed full build-log capture — stdout + stderr per
 //! `nixos-container` / `nix build` invocation, accumulated live.
 //! Schema, indices, retention, and the rationale for replacing
-//! the old ring buffer: `docs/2-handbook/agents/persistence.md::/var/lib/hyperhive/db/build_logs.sqlite`.
+//! the old ring buffer: `docs/4-implementation/agent-state/persistence.md::/var/lib/hyperhive/db/build_logs.sqlite`.
 
 use std::path::Path;
 use std::sync::{Arc, Mutex, OnceLock};

hive-c0re/src/workers/crash_watch.rs

@@ -4,7 +4,7 @@
 //! that line directly; see the module doc on [`emit_crash_transitions`].
 //! Login-state transitions (`needs_login`/`logged_in`) publish onto
 //! `swarm_notices` instead. The `RECENT_TRANSIENT_GRACE` window:
-//! `docs/2-handbook/agents/config-changes.md::System messages`.
+//! `docs/4-implementation/agent-state/config-changes.md::System messages`.
 
 use std::collections::HashSet;
 use std::sync::Arc;