final docs + cleanup sync for meta-flake era

claude.md flips 'in flight' → 'just landed' for the meta
overhaul + extends the file map with meta.rs and migrate.rs.
docs/approvals.md replaces the in-flight callout with a
proper 'Meta flake' section (two-phase deploy walkthrough,
sync_agents semantics, single-phase variants), updates the
two-repo box diagram to include the /var/lib/hyperhive/meta/
tree and tracks flake.nix in applied, rewrites the
container --flake reference to meta#<name>, replaces the
'Manager view of applied' section with a unified
'/agents + /applied + /meta' inventory listing every useful
git incantation, and explains the in-place no-state-loss
migration that now runs on hive-c0re startup.
docs/persistence.md grows entries for the meta repo + the
.meta-migration-done marker. readme box diagram picks up the
/meta RO bind; approval-flow paragraph rewritten end to end
to describe the meta lock dance.

lifecycle::flake_base deleted — the meta render hardcodes
the manager vs agent-base choice as nix expression.

hive-c0re/src/lifecycle.rs

@@ -80,20 +80,6 @@ pub fn is_manager(name: &str) -> bool {
     name == MANAGER_NAME
 }
 
-/// The nixosConfiguration in the hyperhive flake the agent's
-/// wrapper extends. Manager → `manager`; everyone else →
-/// `agent-base`. Used by the meta-flake generator to know which
-/// base to extend per agent.
-#[must_use]
-#[allow(dead_code)] // wired up by the meta module in a follow-up commit
-pub fn flake_base(name: &str) -> &'static str {
-    if is_manager(name) {
-        "manager"
-    } else {
-        "agent-base"
-    }
-}
-
 fn validate(name: &str) -> Result<()> {
     if name.is_empty() {
         bail!("agent name must not be empty");