Safer tools.func load and improved error handling

Replace process-substitution sourcing of tools.func with an explicit curl -> variable -> source via /dev/stdin, adding failure messages and a check that expected functions (e.g. fetch_and_deploy_gh_release) are present (misc/alpine-install.func, misc/install.func). Add categorize_error mapping for exit code 10 -> "config" (misc/api.func). Tweak build.func: minor pipeline formatting and change the ERR trap to capture the actual exit code and only call ensure_log_on_host/post_update on non-zero exits, preventing erroneous failure reporting.

misc/api.func

@@ -875,6 +875,9 @@ categorize_error() {
   # Network errors (curl/wget)
   6 | 7 | 22 | 35) echo "network" ;;
 
+  # Docker / Privileged mode required
+  10) echo "config" ;;
+
   # Timeout errors
   28 | 124 | 211) echo "timeout" ;;