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/install.func

@@ -51,7 +51,9 @@ get_lxc_ip
 # post_progress_to_api()
 #
 # - Lightweight progress ping from inside the container
-# - Updates the existing telemetry record status from "installing" to "configuring"
+# - Updates the existing telemetry record status
+# - Arguments:
+#   * $1: status (optional, default: "configuring")
 # - Signals that the installation is actively progressing (not stuck)
 # - Fire-and-forget: never blocks or fails the script
 # - Only executes if DIAGNOSTICS=yes and RANDOM_UUID is set
@@ -61,9 +63,11 @@ post_progress_to_api() {
   [[ "${DIAGNOSTICS:-no}" == "no" ]] && return 0
   [[ -z "${RANDOM_UUID:-}" ]] && return 0
 
+  local progress_status="${1:-configuring}"
+
   curl -fsS -m 5 -X POST "https://telemetry.community-scripts.org/telemetry" \
     -H "Content-Type: application/json" \
-    -d "{\"random_id\":\"${RANDOM_UUID}\",\"execution_id\":\"${EXECUTION_ID:-${RANDOM_UUID}}\",\"type\":\"lxc\",\"nsapp\":\"${app:-unknown}\",\"status\":\"configuring\"}" &>/dev/null || true
+    -d "{\"random_id\":\"${RANDOM_UUID}\",\"execution_id\":\"${EXECUTION_ID:-${RANDOM_UUID}}\",\"type\":\"lxc\",\"nsapp\":\"${app:-unknown}\",\"status\":\"${progress_status}\"}" &>/dev/null || true
 }
 
 # ==============================================================================