add auto-detect upstream, install script, release workflow

- Default upstream auto-detected from system resolver (scutil/resolv.conf)
  instead of hardcoding Google 8.8.8.8. Falls back to Quad9 (9.9.9.9).
- Single scutil --dns pass for both upstream detection and forwarding rules
- Linux: reads backup resolv.conf if current only has loopback
- Service start/stop now couples DNS config (install on start, uninstall on stop)
- Install script for one-line binary install from GitHub Releases
- GitHub Actions release workflow: builds for macOS/Linux x86_64/aarch64

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

install.sh

@@ -0,0 +1,71 @@
+#!/bin/sh
+# Numa installer — detects OS/arch and downloads the latest release
+# Usage: curl -sSL https://raw.githubusercontent.com/razvandimescu/numa/main/install.sh | sh
+set -e
+
+REPO="razvandimescu/numa"
+INSTALL_DIR="/usr/local/bin"
+
+# Detect OS
+OS="$(uname -s)"
+case "$OS" in
+  Darwin) OS_NAME="macos" ;;
+  Linux)  OS_NAME="linux" ;;
+  *)      echo "Unsupported OS: $OS"; exit 1 ;;
+esac
+
+# Detect architecture
+ARCH="$(uname -m)"
+case "$ARCH" in
+  x86_64|amd64)  ARCH_NAME="x86_64" ;;
+  arm64|aarch64) ARCH_NAME="aarch64" ;;
+  *)             echo "Unsupported architecture: $ARCH"; exit 1 ;;
+esac
+
+ASSET="numa-${OS_NAME}-${ARCH_NAME}.tar.gz"
+
+echo ""
+echo "  \033[1;38;2;192;98;58mNuma\033[0m installer"
+echo ""
+echo "  OS:   $OS_NAME"
+echo "  Arch: $ARCH_NAME"
+echo ""
+
+# Get latest release tag
+echo "  Fetching latest release..."
+TAG=$(curl -sSL "https://api.github.com/repos/${REPO}/releases/latest" | grep '"tag_name"' | head -1 | sed 's/.*"tag_name": *"\([^"]*\)".*/\1/')
+
+if [ -z "$TAG" ]; then
+  echo "  Error: could not find latest release."
+  echo "  Check https://github.com/${REPO}/releases"
+  exit 1
+fi
+
+URL="https://github.com/${REPO}/releases/download/${TAG}/${ASSET}"
+echo "  Downloading ${TAG}..."
+
+# Download and extract
+TMP=$(mktemp -d)
+curl -sSL "$URL" -o "$TMP/$ASSET"
+tar xzf "$TMP/$ASSET" -C "$TMP"
+
+# Install
+if [ -w "$INSTALL_DIR" ]; then
+  mv "$TMP/numa" "$INSTALL_DIR/numa"
+else
+  echo "  Installing to $INSTALL_DIR (requires sudo)..."
+  sudo mv "$TMP/numa" "$INSTALL_DIR/numa"
+fi
+
+chmod +x "$INSTALL_DIR/numa"
+rm -rf "$TMP"
+
+echo ""
+echo "  \033[38;2;107;124;78mInstalled:\033[0m $INSTALL_DIR/numa ($TAG)"
+echo ""
+echo "  Get started:"
+echo "    sudo numa                    # start the DNS server"
+echo "    sudo numa install            # set as system DNS"
+echo "    sudo numa service start      # run as persistent service"
+echo "    open http://localhost:5380    # dashboard"
+echo ""