common: rename --tensor-read-lazy to --lazy-mode, add -lzm shorthand (#27969)

Rename the --tensor-read-lazy CLI argument to --lazy-mode, to match the
internal lazy_mode parameter, and add a -lzm shorthand. Sync the READMEs.

Assisted-by: pi:llama.cpp/Qwen3.8-27B

common/arg.cpp

@@ -2729,7 +2729,7 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
         }
     ).set_env("LLAMA_ARG_LOAD_MODE"));
     add_opt(common_arg(
-        {"--tensor-read-lazy"}, "MODE",
+        {"-lzm", "--lazy-mode"}, "MODE",
         "on-demand reading of certain tensors, for example per-layer embeddings (default: auto)\n"
         "- on: read the rows of such tensors from disk on demand instead of keeping them resident (requires mmap)\n"
         "- auto: on, but only for tensors larger than 4 GiB\n"
@@ -2740,7 +2740,7 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
             else if (value == "off")  { params.lazy_mode = LLAMA_LAZY_MODE_OFF;  }
             else { throw std::invalid_argument("invalid value"); }
         }
-    ).set_env("LLAMA_ARG_TENSOR_READ_LAZY"));
+    ).set_env("LLAMA_ARG_LAZY_MODE"));
     add_opt(common_arg(
         {"--numa"}, "TYPE",
         "attempt optimizations that help on some NUMA systems\n"