refactor: v0.8 Iteration B — cruft purge + ALPN bump to itsgoin/4

Zero-users ruling removes all wire-compat obligations. Net -1,443 LOC of Rust.

Protocol break:
- ALPN_V2 b"itsgoin/3" -> ALPN b"itsgoin/4" (renamed: the versioned name was
  what rotted). Old nodes are now refused at the QUIC handshake instead of
  half-interoperating with the v0.8 manifest/digest formats. Deploy gate from
  Iteration A is discharged.

Dead wire surface removed (MessageType 46 -> 40):
- DeleteRecord 0x51 (deletes ride ControlOp::DeletePost + InitialExchange)
- VisibilityUpdate 0x52 + its two dead senders (ControlOp::UpdateVisibility)
- SocialDisconnectNotice 0x71 (zero senders; checkin timeouts carry the signal)
- MeshPrefer 0xB3 + request_prefer + handler (preferred peers are gone)
- Legacy dual pull-matching half (have_post_ids) — behavior-identical
- PullSyncResponse.visibility_updates + counters (control posts cover it)
- serde(default) stripped from wire-only payloads (kept where
  skip_serializing_if makes it load-bearing; persisted-row defaults untouched)

Preferred-peer subsystem eliminated (design ruling: CDN file_holders replaced
the N+10 direct push/pull it served): slot tier, preferred_peers table (dropped),
preferred_tree semantics, rebalance Priority 0, find_relays_for preferred tiers,
7-day prune + 30-day watcher, dead FromStr impl. Slots are now Local/Wide only
(91 desktop / 12 mobile) pending Iteration C's single ~20-slot pool.

Other dead code: hostlist encoder + base64url helper, always-empty
downstream_addrs parameter chain, start_upnp_renewal_cycle no-op + 4 callers,
RELAY_TARGET_RATE_LIMIT, GetSecretSeed, stale comments swept.

Preserved deliberately: EDM scanner corpse (awaiting raw-UDP refactor),
PortScanHeartbeat, Iteration A startup migrations, session-relay opt-in gating.

Docs: design.html + tech.html synced (message counts, ALPN, purge status,
Rework asides flipped past-tense).

190 core tests pass; CLI + desktop build; A3 integration 9/9 (independently
re-run post-purge).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LGiPD2cF75mnvneSCjdDC5

crates/tauri-app/src/lib.rs

@@ -2493,7 +2493,6 @@ async fn sync_from_peer(state: State<'_, AppNode>, node_id_hex: String) -> Resul
 #[derive(Serialize)]
 #[serde(rename_all = "camelCase")]
 struct NetworkSummaryDto {
-    preferred_count: usize,
     local_count: usize,
     wide_count: usize,
     total_connections: usize,
@@ -2508,12 +2507,10 @@ struct NetworkSummaryDto {
 async fn get_network_summary(state: State<'_, AppNode>) -> Result<NetworkSummaryDto, String> {
     let node = get_node(&state).await;
     let conns = node.list_connections().await;
-    let mut preferred = 0usize;
     let mut local = 0usize;
     let mut wide = 0usize;
     for (_nid, slot_kind, _at) in &conns {
         match slot_kind {
-            PeerSlotKind::Preferred => preferred += 1,
             PeerSlotKind::Local => local += 1,
             PeerSlotKind::Wide => wide += 1,
         }
@@ -2525,7 +2522,6 @@ async fn get_network_summary(state: State<'_, AppNode>) -> Result<NetworkSummary
         (n2, n3)
     };
     Ok(NetworkSummaryDto {
-        preferred_count: preferred,
         local_count: local,
         wide_count: wide,
         total_connections: conns.len(),
@@ -3201,14 +3197,13 @@ async fn switch_identity(
 
     // Start background tasks on the new node
     new_node.start_accept_loop();
-    new_node.start_pull_cycle(300);
+    new_node.start_pull_cycle();
     new_node.start_diff_cycle(120);
     new_node.start_rebalance_cycle(600);
     new_node.start_growth_loop();
     new_node.start_recovery_loop();
     new_node.start_social_checkin_cycle(3600);
     new_node.start_anchor_register_cycle(600);
-    new_node.start_upnp_renewal_cycle();
     new_node.start_upnp_tcp_renewal_cycle();
     new_node.start_http_server();
     new_node.start_bootstrap_connectivity_check();
@@ -3326,14 +3321,13 @@ async fn clear_duplicate_flag(state: State<'_, AppNode>) -> Result<(), String> {
     node.network.duplicate_detected.store(false, std::sync::atomic::Ordering::Relaxed);
     // Start the sync tasks that were skipped during bootstrap
     node.start_accept_loop();
-    node.start_pull_cycle(300);
+    node.start_pull_cycle();
     node.start_diff_cycle(120);
     node.start_rebalance_cycle(600);
     node.start_growth_loop();
     node.start_recovery_loop();
     node.start_social_checkin_cycle(3600);
     node.start_anchor_register_cycle(600);
-    node.start_upnp_renewal_cycle();
     node.start_upnp_tcp_renewal_cycle();
     node.start_http_server();
     node.start_bootstrap_connectivity_check();
@@ -3575,14 +3569,13 @@ pub fn run() {
 
                 // Start all background networking tasks
                 boot_node.start_accept_loop();
-                boot_node.start_pull_cycle(300);
+                boot_node.start_pull_cycle();
                 boot_node.start_diff_cycle(120);
                 boot_node.start_rebalance_cycle(600);
                 boot_node.start_growth_loop();
                 boot_node.start_recovery_loop();
                 boot_node.start_social_checkin_cycle(3600);
                 boot_node.start_anchor_register_cycle(600);
-                boot_node.start_upnp_renewal_cycle();
                 boot_node.start_upnp_tcp_renewal_cycle();
                 boot_node.start_http_server();
                 boot_node.start_bootstrap_connectivity_check();