core: remove old Go API and extend misc/api.func with new backend (#11822)

* Remove Go API and extend misc/api.func

Delete the Go-based API (api/main.go, api/go.mod, api/go.sum, api/.env.example) and significantly enhance misc/api.func. The shell telemetry file now includes telemetry configuration, repo source detection, GPU/CPU/RAM detection, expanded explain_exit_code mappings, and refactored post_to_api/post_to_api_vm to send non-blocking telemetry to telemetry.community-scripts.org while respecting DIAGNOSTICS/DEV_MODE and adding richer metadata (cpu/gpu/ram/repo_source). Also updates header/author info and improves privacy/robustness and error handling.

* Start install timer and refine error reporting

Call start_install_timer during build startup and overhaul exit/error reporting.

Changes:
- Invoke start_install_timer early in misc/build.func to track install duration.
- Update api_exit_script comments to reference PocketBase/api.func and adjust ERR/SIGINT/SIGTERM traps to post numeric exit codes (use $? / 130 / 143) instead of command strings.
- Replace the previous explain_exit_code implementation with a conditional fallback: only define explain_exit_code if not already provided (api.func is the canonical source). Expanded and reorganized exit code mappings (curl, timeout, systemd, Node/Python/Postgres/MySQL/MongoDB, Proxmox, etc.).
- In error_handler: stop echoing the container log path (host shows combined log), and post a "failed" update to the API with the exit code before offering container cleanup.

Rationale: these changes make telemetry more consistent and robust (numeric codes), provide a safe fallback for exit descriptions when api.func isn't loaded, and ensure failures are reported to the API prior to any automatic cleanup.

* Report install start/failure to telemetry API

Add telemetry hooks in misc/build.func: call post_to_api at installation start to capture early or immediately-failing installs, and call post_update_to_api with status "failed" and the install exit code when a container installation fails. This improves visibility into install failures for monitoring/telemetry.

misc/build.func

@@ -3636,6 +3636,9 @@ $PCT_OPTIONS_STRING"
       exit 214
     fi
     msg_ok "Storage space validated"
+
+    # Report installation start to API (early - captures failed installs too)
+    post_to_api
   fi
 
   create_lxc_container || exit $?
@@ -4010,6 +4013,9 @@ EOF'
   # Install SSH keys
   install_ssh_keys_into_ct
 
+  # Start timer for duration tracking
+  start_install_timer
+
   # Run application installer
   # Disable error trap - container errors are handled internally via flag file
   set +Eeuo pipefail # Disable ALL error handling temporarily
@@ -4040,6 +4046,9 @@ EOF'
   if [[ $install_exit_code -ne 0 ]]; then
     msg_error "Installation failed in container ${CTID} (exit code: ${install_exit_code})"
 
+    # Report failure to telemetry API
+    post_update_to_api "failed" "$install_exit_code"
+  
     # Copy both logs from container before potential deletion
     local build_log_copied=false
     local install_log_copied=false
@@ -5123,9 +5132,9 @@ EOF
 # api_exit_script()
 #
 # - Exit trap handler for reporting to API telemetry
-# - Captures exit code and reports to API using centralized error descriptions
-# - Uses explain_exit_code() from error_handler.func for consistent error messages
-# - Posts failure status with exit code to API (error description added automatically)
+# - Captures exit code and reports to PocketBase using centralized error descriptions
+# - Uses explain_exit_code() from api.func for consistent error messages
+# - Posts failure status with exit code to API (error description resolved automatically)
 # - Only executes on non-zero exit codes
 # ------------------------------------------------------------------------------
 api_exit_script() {
@@ -5138,6 +5147,6 @@ api_exit_script() {
 if command -v pveversion >/dev/null 2>&1; then
   trap 'api_exit_script' EXIT
 fi
-trap 'post_update_to_api "failed" "$BASH_COMMAND"' ERR
-trap 'post_update_to_api "failed" "INTERRUPTED"' SIGINT
-trap 'post_update_to_api "failed" "TERMINATED"' SIGTERM
+trap 'post_update_to_api "failed" "$?"' ERR
+trap 'post_update_to_api "failed" "130"' SIGINT
+trap 'post_update_to_api "failed" "143"' SIGTERM