feat: add command line arguments to install script (addresses #324)

The install script now accepts arguments that work with piped execution:
- --rc or --pre: Install latest RC/pre-release
- --stable: Force stable version (default)
- --version VERSION: Install specific version
- --help: Show usage

This allows users to update to RC versions with:
curl -fsSL .../install.sh | bash -s -- --rc

install.sh

@@ -146,37 +146,49 @@ backup_existing() {
 download_pulse() {
     print_info "Downloading Pulse..."
     
-    # Check if user has RC channel configured
-    UPDATE_CHANNEL="stable"
-    
-    # Allow override via environment variable
-    if [[ "${PULSE_UPDATE_CHANNEL:-}" == "rc" ]]; then
-        UPDATE_CHANNEL="rc"
-        print_info "RC channel requested via environment variable"
-    elif [[ -f "$CONFIG_DIR/system.json" ]]; then
-        CONFIGURED_CHANNEL=$(cat "$CONFIG_DIR/system.json" 2>/dev/null | grep -o '"updateChannel"[[:space:]]*:[[:space:]]*"[^"]*"' | sed 's/.*"\([^"]*\)"$/\1/')
-        if [[ "$CONFIGURED_CHANNEL" == "rc" ]]; then
-            UPDATE_CHANNEL="rc"
-            print_info "RC channel detected in configuration"
+    # Check for forced version first
+    if [[ -n "${FORCE_VERSION}" ]]; then
+        LATEST_RELEASE="${FORCE_VERSION}"
+        print_info "Installing specific version: $LATEST_RELEASE"
+        
+        # Verify the version exists
+        if ! curl -fsS "https://api.github.com/repos/$GITHUB_REPO/releases/tags/$LATEST_RELEASE" > /dev/null 2>&1; then
+            print_error "Version $LATEST_RELEASE not found"
+            exit 1
         fi
-    fi
-    
-    # Get appropriate release based on channel
-    if [[ "$UPDATE_CHANNEL" == "rc" ]]; then
-        # Get all releases and find the latest (including pre-releases)
-        LATEST_RELEASE=$(curl -s https://api.github.com/repos/$GITHUB_REPO/releases | grep '"tag_name":' | head -1 | sed -E 's/.*"([^"]+)".*/\1/')
     else
-        # Get latest stable release only
-        LATEST_RELEASE=$(curl -s https://api.github.com/repos/$GITHUB_REPO/releases/latest | grep '"tag_name":' | sed -E 's/.*"([^"]+)".*/\1/')
+        # Check if user has RC channel configured
+        UPDATE_CHANNEL="stable"
+        
+        # Allow override via command line
+        if [[ -n "${FORCE_CHANNEL}" ]]; then
+            UPDATE_CHANNEL="${FORCE_CHANNEL}"
+            print_info "Using $UPDATE_CHANNEL channel from command line"
+        elif [[ -f "$CONFIG_DIR/system.json" ]]; then
+            CONFIGURED_CHANNEL=$(cat "$CONFIG_DIR/system.json" 2>/dev/null | grep -o '"updateChannel"[[:space:]]*:[[:space:]]*"[^"]*"' | sed 's/.*"\([^"]*\)"$/\1/')
+            if [[ "$CONFIGURED_CHANNEL" == "rc" ]]; then
+                UPDATE_CHANNEL="rc"
+                print_info "RC channel detected in configuration"
+            fi
+        fi
+        
+        # Get appropriate release based on channel
+        if [[ "$UPDATE_CHANNEL" == "rc" ]]; then
+            # Get all releases and find the latest (including pre-releases)
+            LATEST_RELEASE=$(curl -s https://api.github.com/repos/$GITHUB_REPO/releases | grep '"tag_name":' | head -1 | sed -E 's/.*"([^"]+)".*/\1/')
+        else
+            # Get latest stable release only
+            LATEST_RELEASE=$(curl -s https://api.github.com/repos/$GITHUB_REPO/releases/latest | grep '"tag_name":' | sed -E 's/.*"([^"]+)".*/\1/')
+        fi
+        
+        if [[ -z "$LATEST_RELEASE" ]]; then
+            print_error "Could not determine latest release"
+            exit 1
+        fi
+        
+        print_info "Latest version: $LATEST_RELEASE"
     fi
     
-    if [[ -z "$LATEST_RELEASE" ]]; then
-        print_error "Could not determine latest release"
-        exit 1
-    fi
-    
-    print_info "Latest version: $LATEST_RELEASE"
-    
     # Detect architecture
     ARCH=$(uname -m)
     case $ARCH in
@@ -392,5 +404,43 @@ main() {
     fi
 }
 
+# Parse command line arguments
+FORCE_VERSION=""
+FORCE_CHANNEL=""
+
+while [[ $# -gt 0 ]]; do
+    case $1 in
+        --rc|--pre|--prerelease)
+            FORCE_CHANNEL="rc"
+            shift
+            ;;
+        --stable)
+            FORCE_CHANNEL="stable"
+            shift
+            ;;
+        --version)
+            FORCE_VERSION="$2"
+            shift 2
+            ;;
+        -h|--help)
+            echo "Usage: $0 [OPTIONS]"
+            echo "Options:"
+            echo "  --rc, --pre        Install latest RC/pre-release version"
+            echo "  --stable           Install latest stable version (default)"
+            echo "  --version VERSION  Install specific version (e.g., v4.4.0-rc.1)"
+            echo "  -h, --help         Show this help message"
+            exit 0
+            ;;
+        *)
+            print_error "Unknown option: $1"
+            echo "Use --help for usage information"
+            exit 1
+            ;;
+    esac
+done
+
+# Export for use in download_pulse function
+export FORCE_VERSION FORCE_CHANNEL
+
 # Run main function
-main "$@"
+main