feat(mini): add compact native EasyTier client (#2479)

Add a native EasyTier proof-of-concept binary with TCP and UDP
transports, TUN, UDP hole punching, AES-GCM, and a read-only RPC
portal.

Introduce a release-derived mini profile and musl linker policy so
x86_64, big-endian MIPS, and little-endian MIPS stay below the strict
5,000,000-byte target without UPX.

easytier-contrib/easytier-mini/build-mips.sh

@@ -0,0 +1,61 @@
+#!/bin/sh
+set -eu
+
+# Cargo invokes this same file as a rustc wrapper during compact MIPS builds.
+# Applying immediate-abort here keeps the size policy scoped to easytier-mini;
+# normal MIPS builds elsewhere in the workspace retain their panic behavior.
+if [ "${EASYTIER_MINI_MIPS_RUSTC_WRAPPER:-}" = "1" ]; then
+    mini_rustc=$1
+    shift
+    for mini_rustc_arg in "$@"; do
+        case "$mini_rustc_arg" in
+            mips-unknown-linux-musl|mipsel-unknown-linux-musl)
+                exec "$mini_rustc" "$@" \
+                    -Zunstable-options \
+                    -Cpanic=immediate-abort
+                ;;
+        esac
+    done
+    exec "$mini_rustc" "$@"
+fi
+
+mini_script_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+mini_repo_dir=$(CDPATH= cd -- "$mini_script_dir/../.." && pwd)
+mini_requested_target=${1:-all}
+cd "$mini_repo_dir"
+
+build_mips_target() {
+    mini_target=$1
+    mini_toolchain=$2
+    PATH="$mini_repo_dir/musl_gcc/$mini_toolchain/bin:$PATH" \
+        EASYTIER_MINI_MIPS_RUSTC_WRAPPER=1 \
+        RUSTC_BOOTSTRAP=1 \
+        RUSTC_WRAPPER="$mini_script_dir/build-mips.sh" \
+        cargo build \
+            --manifest-path "$mini_repo_dir/Cargo.toml" \
+            --profile mini \
+            --target "$mini_target" \
+            -Z build-std=std \
+            -Z build-std-features=optimize_for_size \
+            -p easytier-mini
+}
+
+case "$mini_requested_target" in
+    all)
+        build_mips_target mips-unknown-linux-musl mips-unknown-linux-muslsf
+        build_mips_target mipsel-unknown-linux-musl mipsel-unknown-linux-muslsf
+        ;;
+    mips|mips-unknown-linux-musl)
+        build_mips_target mips-unknown-linux-musl mips-unknown-linux-muslsf
+        ;;
+    mipsel|mipsel-unknown-linux-musl)
+        build_mips_target mipsel-unknown-linux-musl mipsel-unknown-linux-muslsf
+        ;;
+    -h|--help)
+        echo "usage: $0 [all|mips|mipsel]"
+        ;;
+    *)
+        echo "unsupported MIPS target: $mini_requested_target" >&2
+        exit 2
+        ;;
+esac