core-refactor: single-reporter telemetry rewrite (#15933)

Overhaul the telemetry system to enforce a single-reporter model where only the HOST sends terminal statuses (success/failed/aborted) to the API. Containers now write local artifact files (.failed flag + .errinfo) that the host picks up after lxc-attach returns, preventing the race condition where a metadata-less container payload would win over the full host payload.

Key changes:
- Add TELEMETRY_CONTEXT=container export in install.func/alpine-install.func to mark container context before error handling starts
- Introduce _is_container_context() heuristic and _container_write_failure() artifact writer in error_handler.func
- Refactor api.func: unified _tm_payload() builder (full metadata on every send), _tm_send() curl wrapper, _tm_enabled() gate, telemetry_collect_sysinfo() cached collector
- Add structured .errinfo capture in silent() (core.func) using byte-offset to extract exactly the failing command's output
- Pull .errinfo from container in build.func after lxc-attach for precise error traces
- Add categorize_error(), telemetry_new_attempt(), detect_arm(), REPO_SLUG tracking
- Signal exits (129/130/143) now report as 'aborted' instead of 'failed'
- Remove post_update_to_api_extended() (superseded by unified _tm_payload)
- Export REPO_SOURCE, REPO_SLUG, TELEMETRY_PLATFORM into container environment

misc/alpine-install.func

@@ -6,6 +6,10 @@
 if ! command -v curl >/dev/null 2>&1; then
   apk update && apk add curl >/dev/null 2>&1
 fi
+# Mark container context BEFORE error handling starts: error_handler/on_exit
+# must write local failure artifacts instead of talking to the telemetry API
+# (the host is the single telemetry reporter).
+export TELEMETRY_CONTEXT="container"
 source <(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVE/main/misc/core.func)
 source <(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVE/main/misc/error_handler.func)
 load_functions
@@ -41,7 +45,7 @@ post_progress_to_api() {
 
   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\":\"${progress_status}\"}" &>/dev/null || true
+    -d "{\"random_id\":\"${RANDOM_UUID}\",\"execution_id\":\"${EXECUTION_ID:-${RANDOM_UUID}}\",\"type\":\"lxc\",\"nsapp\":\"${app:-unknown}\",\"status\":\"${progress_status}\",\"platform\":\"${TELEMETRY_PLATFORM:-}\",\"repo_source\":\"${REPO_SOURCE:-}\",\"repo_slug\":\"${REPO_SLUG:-}\"}" &>/dev/null || true
 }
 
 # This function enables IPv6 if it's not disabled and sets verbose mode