Human-readable peer identifiers in log messages

Replace raw NodeAddr hex strings in log output with human-readable
identifiers using a four-tier lookup: configured alias, active peer
short npub, session endpoint short npub, or truncated hex fallback.

- Add PeerIdentity::short_npub() for compact npub display (npub1xxxx...yyyy)
- Add NodeAddr::short_hex() for compact hex fallback (first 4 bytes + ...)
- Add peer_aliases map populated at startup from peer config
- Add Node::peer_display_name() with four-tier resolution
- Add SessionEntry::remote_pubkey() accessor for session-layer lookups
- Update all 120 log field occurrences across 11 handler/node files
- Pass pre-computed display names to MMP static metric/teardown methods
  to work around borrow checker constraints in iterator loops

src/node/session.rs

@@ -47,7 +47,6 @@ pub(crate) struct SessionEntry {
     #[allow(dead_code)]
     remote_addr: NodeAddr,
     /// Remote node's static public key (for Noise IK).
-    #[allow(dead_code)]
     remote_pubkey: PublicKey,
     /// Current session state. `None` only during state transitions.
     state: Option<EndToEndState>,
@@ -95,6 +94,11 @@ impl SessionEntry {
         }
     }
 
+    /// Get the remote node's public key.
+    pub(crate) fn remote_pubkey(&self) -> &PublicKey {
+        &self.remote_pubkey
+    }
+
     /// Get the current session state.
     pub(crate) fn state(&self) -> &EndToEndState {
         self.state.as_ref().expect("session state taken but not restored")