Add pre/post build stages, fix exec timeout, expand guest PATH

Build phases:
- Pre-build (apt update) and post-build (apt clean, autoremove, rm lists)
  run with 10-minute timeout; user recipe commands keep 30s timeout
- Log entries include phase field for UI grouping
- Always send explicit TimeoutSec to host agent (0 defaulted to 30s)

Frontend:
- Pre-build/post-build steps show phase label without exposing commands
- Recipe steps numbered independently starting from 1

Guest PATH:
- Add /usr/games:/usr/local/games to wrenn-init.sh PATH export
  (standard Ubuntu paths, needed for packages like cowsay)

images/wrenn-init.sh

@@ -25,7 +25,7 @@ echo "nameserver 8.8.8.8" > /etc/resolv.conf
 echo "nameserver 8.8.4.4" >> /etc/resolv.conf
 
 # Set a standard PATH so envd and all child processes can find common binaries.
-export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
 
 # Write chrony config to sync time from the KVM PTP hardware clock.
 # /dev/ptp0 is a paravirtual clock exposed by KVM — no network required.