feat: refactor online update to synchronous web-process download

- Download happens in web process (non-root) with real-time progress
- Root runner only handles privileged apply (stop/backup/switch/restart)
- Eliminates 'waiting for system scheduler' stuck state
- Frontend shows download bytes/speed/percentage with cancel button
- Staged download triggers apply request file for root runner
- systemd timeout reduced from 32min to 5min (no download phase)
- Tests adapted for synchronous download flow
release: 1.3.0

systemd/tallynote-update.service

@@ -10,10 +10,10 @@ ExecStart=/usr/local/libexec/tallynote-update-runner
 Environment=PATH=/usr/sbin:/usr/bin:/sbin:/bin
 # The runner consumes queued requests immediately and applies its own bounded
 # phase timeouts while keeping full CLI diagnostics in the runner log.
-# Downloads, archive validation and data backups can exceed systemd's 90s
+# Archive validation and data backups can exceed systemd's 90s
 # default start timeout on a slower server. Keep one update job alive long
 # enough to finish or reach its own health-check/recovery path.
-TimeoutStartSec=32min
+TimeoutStartSec=5min
 NoNewPrivileges=true
 # Keep the updater compatible with the same Node/libuv interface discovery
 # path while retaining an explicit socket-family allowlist.