feat(install): add Windows PATH persistence via registry

Add support for persistently adding the install directory to the Windows user PATH via the registry. This works from Git Bash (MINGW64), MSYS2, and Cygwin, converting paths appropriately and using PowerShell to modify the registry. Also adds to the current session's PATH for immediate use.

install

@@ -385,6 +385,57 @@ add_to_path() {
     fi
 }
 
+# Persistently add $INSTALL_DIR to the Windows user PATH via the registry.
+# Works from Git Bash (MINGW64), MSYS2, and Cygwin.
+# Converts the MSYS/Cygwin path to native Windows form so that cmd and
+# PowerShell also see the entry.
+add_to_windows_path() {
+    local win_install_dir
+    if command -v cygpath >/dev/null 2>&1; then
+        win_install_dir=$(cygpath -w "$INSTALL_DIR")
+    else
+        # Fallback: naive conversion  /c/Users/... -> C:\Users\...
+        win_install_dir=$(echo "$INSTALL_DIR" | sed -e 's|^/\([a-zA-Z]\)/|\1:\\|' -e 's|/|\\|g')
+    fi
+
+    # Escape single-quotes for PowerShell single-quoted strings ('' is the escape sequence)
+    local win_install_dir_ps="${win_install_dir//\'/\'\'}"
+
+    local ps_cmd
+    ps_cmd=$(cat <<EOFPS
+\$kiloPath = '$win_install_dir_ps'
+\$currentPath = [Environment]::GetEnvironmentVariable('Path', 'User')
+\$pathParts = if ([string]::IsNullOrEmpty(\$currentPath)) { @() } else { \$currentPath -split ';' }
+if (\$pathParts -notcontains \$kiloPath) {
+    \$newPath = if ([string]::IsNullOrEmpty(\$currentPath)) { \$kiloPath } else { "\$currentPath;\$kiloPath" }
+    [Environment]::SetEnvironmentVariable('Path', \$newPath, 'User')
+    Write-Output 'added'
+}
+EOFPS
+)
+
+    local ps_output
+    if command -v powershell.exe >/dev/null 2>&1; then
+        ps_output=$(powershell.exe -NoProfile -NonInteractive -Command "$ps_cmd" 2>/dev/null) || return 1
+    elif command -v pwsh >/dev/null 2>&1; then
+        ps_output=$(pwsh -NoProfile -NonInteractive -Command "$ps_cmd" 2>/dev/null) || return 1
+    else
+        return 1
+    fi
+
+    if [[ "$ps_output" == *"added"* ]]; then
+        print_message info "${MUTED}Successfully added ${NC}kilo ${MUTED}to Windows user PATH${NC}"
+    fi
+
+    # Also add to the current bash session so `kilo` works immediately
+    # without the user needing to open a new terminal.
+    if [[ ":$PATH:" != *":$INSTALL_DIR:"* ]]; then
+        export PATH="$INSTALL_DIR:$PATH"
+    fi
+
+    return 0
+}
+
 XDG_CONFIG_HOME=${XDG_CONFIG_HOME:-$HOME/.config}
 
 current_shell=$(basename "$SHELL")
@@ -411,6 +462,13 @@ case $current_shell in
 esac
 
 if [[ "$no_modify_path" != "true" ]]; then
+    # Detect if we are running on Windows (MINGW, MSYS, Cygwin) regardless
+    # of whether the binary was installed from download or --binary.
+    _running_on_windows=false
+    case "$(uname -s)" in
+        MINGW*|MSYS*|CYGWIN*) _running_on_windows=true ;;
+    esac
+
     config_file=""
     for file in $config_files; do
         if [[ -f $file ]]; then
@@ -419,7 +477,12 @@ if [[ "$no_modify_path" != "true" ]]; then
         fi
     done
 
-    if [[ -z $config_file ]]; then
+    if [[ "$_running_on_windows" == "true" ]] && add_to_windows_path; then
+        # Handled via the Windows user-level PATH in the registry.
+        # The change is visible in new cmd / PowerShell / Git Bash sessions.
+        # We also exported it into the current session above.
+        :
+    elif [[ -z $config_file ]]; then
         print_message warning "No config file found for $current_shell. You may need to manually add to PATH:"
         print_message info "  export PATH=$INSTALL_DIR:\$PATH"
     elif [[ ":$PATH:" != *":$INSTALL_DIR:"* ]]; then