release(v1.7.18-alpha): transitive peers default Trusted + update-flow logs

Flip transitively-discovered federation peers to Trusted instead of
Observer. Hints are already only ingested from peers we trust and only
peers we trust are re-exported via build_local_state, so the chain of
trust is already vetted end-to-end — making the user promote each
newcomer by hand was friction with no security win.

Backend:
- federation/sync.rs: merge_transitive_peers now inserts TrustLevel::Trusted
  (doc comment updated to explain the transitive-trust rationale)
- update.rs: info! log at download start (version, components, total_bytes,
  staging path), cancel (staging wiped?, marker cleared?), and apply (backup
  path) so journalctl reveals where a stuck update actually is

Frontend:
- SystemUpdate What's New block gets a v1.7.18-alpha entry

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

core/archipelago/src/update.rs

@@ -244,6 +244,14 @@ pub async fn download_update(data_dir: &Path) -> Result<DownloadProgress> {
     let mut downloaded = 0u64;
     let total_bytes: u64 = manifest.components.iter().map(|c| c.size_bytes).sum();
 
+    info!(
+        version = %manifest.version,
+        components = manifest.components.len(),
+        total_bytes,
+        staging = %staging_dir.display(),
+        "Starting update download"
+    );
+
     // Clear any stale cancel flag from a prior aborted run, then seed
     // the live counters so polls during the handshake show the right
     // denominator immediately instead of 0/0 → NaN%.
@@ -477,17 +485,27 @@ pub async fn cancel_download(data_dir: &Path) -> Result<()> {
     DOWNLOAD_BYTES.store(0, Ordering::Relaxed);
     DOWNLOAD_TOTAL.store(0, Ordering::Relaxed);
     let staging = data_dir.join("update-staging");
-    if staging.exists() {
-        let _ = tokio::fs::remove_dir_all(&staging).await;
-    }
+    let wiped = if staging.exists() {
+        tokio::fs::remove_dir_all(&staging).await.is_ok()
+    } else {
+        false
+    };
     // Clear the "downloaded, ready to apply" marker too — a canceled
     // download is not a staged update.
+    let mut cleared_marker = false;
     if let Ok(mut state) = load_state(data_dir).await {
         if state.update_in_progress {
             state.update_in_progress = false;
             let _ = save_state(data_dir, &state).await;
+            cleared_marker = true;
         }
     }
+    info!(
+        staging = %staging.display(),
+        wiped,
+        cleared_marker,
+        "Update download canceled"
+    );
     Ok(())
 }
 
@@ -529,6 +547,12 @@ pub async fn apply_update(data_dir: &Path) -> Result<()> {
         .await
         .context("Failed to create backup dir")?;
 
+    info!(
+        staging = %staging_dir.display(),
+        backup = %backup_dir.display(),
+        "Applying staged update"
+    );
+
     // Back up current backend binary
     let current_binary = Path::new("/usr/local/bin/archipelago");
     if current_binary.exists() {