Improve arm64 support and arch-specific downloads

Add clearer architecture error messages and gate arm64 usage, plus implement architecture-aware behavior across the toolkit. Changes include: update exit-code messages to reference amd64/arm64, refuse arm64 unless explicitly enabled, show architecture in summaries, and use arch-specific package lists when installing in containers. Make downloads for FFmpeg and yq choose the correct amd64/arm64 binaries, tighten template download error handling and formatting, and clean up minor whitespace/comment issues. These changes aim to make arm64 handling explicit and downloads/installations more robust for non-amd64 systems.

misc/core.func

@@ -351,6 +351,11 @@ arch_check() {
     sleep 2
     exit 106
   fi
+  if [[ "$arch" == "arm64" && "${var_arm64:-}" != "yes" ]]; then
+    msg_error "This script does not yet support arm64."
+    sleep 2
+    exit 106
+  fi
 }
 
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