feat(fof-layer1): wire types + V_me auto-gen on persona creation

Adds VouchGrantBatch type to types.rs and extends ProfilePostContent
with optional vouch_grants + bio_epoch fields (back-compat via
#[serde(default)]). VouchGrantBatch carries one shared batch_eph_pub
+ a Vec<Vec<u8>> of 48-byte wrappers; receivers identify their wrapper
by AEAD success, not position.

Wires V_me auto-generation into both persona-creation paths:
- Node::open first-run auto-persona block now seeds vouch_keys_own
  epoch=1 alongside upsert_posting_identity.
- create_posting_identity calls ensure_initial_v_me after the new
  persona is stored.

Helpers live as private free functions at module scope so both the
sync (Node::open holds a Storage guard) and async (create_posting
holds a StoragePool) sites can share them. Idempotent — re-running
on a persona that already has a current key is a no-op.

Two existing ProfilePostContent construction sites updated to set the
new fields to defaults (None / 0); they'll get real values when the
publish path is wired up in the next commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/core/src/profile.rs

@@ -88,6 +88,8 @@ pub fn build_profile_post(
         avatar_cid,
         timestamp_ms,
         signature,
+        vouch_grants: None,
+        bio_epoch: 0,
     };
     Post {
         author: *author,