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>

neode-ui/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "neode-ui",
-  "version": "1.3.5",
+  "version": "1.6.0-alpha",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "neode-ui",
-      "version": "1.3.5",
+      "version": "1.6.0-alpha",
       "dependencies": {
         "@types/dompurify": "^3.0.5",
         "@vue-leaflet/vue-leaflet": "^0.10.1",