feat(telemetry): add 'validation' status, fix status transitions, show 20 log lines

Status flow is now: installing → validation → configuring → success/failed

Changes:
- post_progress_to_api() accepts optional status parameter (default: configuring)
- build.func: Send 'validation' before storage/template/cluster checks
- build.func: Send 'configuring' just before lxc-attach (app install)
- build.func: Remove redundant progress pings during container start/network
- install.func + alpine-install.func: Accept status parameter in container-side
  post_progress_to_api()
- core.func + vm-core.func: silent() now shows last 20 lines on error (was 10)

misc/vm-core.func

@@ -169,7 +169,7 @@ get_active_logfile() {
 # silent()
 #
 # - Executes command with output redirected to active log file
-# - On error: displays last 10 lines of log and exits with original exit code
+# - On error: displays last 20 lines of log and exits with original exit code
 # - Temporarily disables error trap to capture exit code correctly
 # - Sources explain_exit_code() for detailed error messages
 # ------------------------------------------------------------------------------
@@ -207,8 +207,8 @@ silent() {
     msg_custom "→" "${YWB}" "${cmd}"
 
     if [[ -s "$logfile" ]]; then
-      echo -e "\n${TAB}--- Last 10 lines of log ---"
-      tail -n 10 "$logfile"
+      echo -e "\n${TAB}--- Last 20 lines of log ---"
+      tail -n 20 "$logfile"
       echo -e "${TAB}----------------------------\n"
     fi