ux: Friend-button default + profile-rename plumbing + export/import clarity

Three of the v0.7.0 device-testing feedback items, deferred for later
rebuild/redeploy (Scott opted to batch UI fixes).

(#1) Friend button on bio modal:
- Primary action when neither following nor vouched: [Friend] (=
  follow + vouch in one click) plus secondary [Follow only].
- When following without a vouch: [Add Vouch] primary, [Unfollow]
  secondary.
- When both follow + vouch (= friends): [Unfriend] (= revoke vouch
  + unfollow, with the rotation-cost confirm wording).
- The standalone [Vouch] / [Revoke Vouch] flows stay reachable from
  the existing Vouches list in Settings.

(#2) Profile shows "unnamed" — bug fix:
- set_profile updated the profiles table + emitted a profile post,
  but never updated posting_identities.display_name. list_posting_
  identities returns from the latter, so the Personas list kept
  showing "(unnamed)" forever after the first-run auto-persona was
  named.
- Now set_profile also upserts the posting_identities row with the
  new display_name (secret_seed + created_at preserved).

(#5) Export/import + persona-vs-device clarity:
- Settings reorder: new "Your data on this device" explainer card up
  top (Personas = who you are to peers; Identities = device's
  network address, rarely useful to touch).
- "Move to another device" section renamed + given a plain-English
  description; primary [Export personas] / [Import from another
  device] buttons.
- "Identities (advanced)" demoted below; warning text added.
- Export wizard heading: "Export your personas"; radio labels use
  persona/keys language consistently.
- Import wizard heading: "Import from another device"; explainer
  notes that the default action restores personas.

Tracking memory created at memory/project_v071_followups.md for
deferred items (#4 PQ vouch delivery, #6 rename, #7 redundancy,
#8/#9/#10 awaiting clarification).

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

crates/core/src/node.rs

@@ -1793,6 +1793,20 @@ impl Node {
                     }
                 }
             }
+            // Keep posting_identities.display_name in sync with the
+            // profile post so the Personas list and any UI reading
+            // PostingIdentity sees the current name (not the original
+            // empty/auto-gen one). The upsert preserves the persona's
+            // secret_seed / created_at; only display_name changes.
+            if let Ok(Some(existing)) = storage.get_posting_identity(&posting_id) {
+                let updated = crate::types::PostingIdentity {
+                    node_id: existing.node_id,
+                    secret_seed: existing.secret_seed,
+                    display_name: display_name.clone(),
+                    created_at: existing.created_at,
+                };
+                let _ = storage.upsert_posting_identity(&updated);
+            }
         }
 
         // Propagate via neighbor-manifest header diffs like any other post.