feat: add interactive setup wizard for first-run configuration

Implement a comprehensive setup wizard to improve onboarding and
configuration experience for both personal and server deployments.

Key features:
- Interactive wizard with profile selection (personal/server/custom)
- Quick setup mode with sensible defaults
- First-run detection with helpful welcome message
- Directory configuration with validation
- Server OAuth/JWT configuration with auto-generation
- Environment file creation for server deployments
- Template generators for systemd service and env files

New commands:
- opal setup              # Interactive wizard
- opal setup --quick      # Quick setup with defaults
- opal setup --profile    # Use specific profile
- opal setup --show-systemd  # Show systemd template
- opal setup --show-env   # Show environment file template

Implementation:
- internal/wizard/prompts.go: Reusable prompt utilities
- internal/wizard/profiles.go: Profile definitions and templates
- cmd/setup.go: Main setup command implementation
- cmd/root.go: First-run detection and welcome message
- internal/engine/config.go: ConfigExists() and IsFirstRun() helpers

User experience:
- On first run, shows welcome message suggesting 'opal setup'
- Non-intrusive - creates defaults automatically if skipped
- Wizard guides through all configuration options
- Server setup includes OAuth/JWT configuration
- Environment file created with proper permissions (0600)
- Clear next steps displayed after completion

opal-task/internal/wizard/prompts.go

@@ -0,0 +1,144 @@
+package wizard
+
+import (
+	"bufio"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// PromptString prompts for a string value with a default
+func PromptString(prompt string, defaultValue string) string {
+	if defaultValue != "" {
+		fmt.Printf("%s [%s]: ", prompt, defaultValue)
+	} else {
+		fmt.Printf("%s: ", prompt)
+	}
+
+	reader := bufio.NewReader(os.Stdin)
+	input, _ := reader.ReadString('\n')
+	input = strings.TrimSpace(input)
+
+	if input == "" {
+		return defaultValue
+	}
+	return input
+}
+
+// PromptPassword prompts for a password (hidden input would be nice, but we'll use simple input for now)
+func PromptPassword(prompt string) string {
+	fmt.Printf("%s: ", prompt)
+	reader := bufio.NewReader(os.Stdin)
+	input, _ := reader.ReadString('\n')
+	return strings.TrimSpace(input)
+}
+
+// PromptBool prompts for a yes/no answer
+func PromptBool(prompt string, defaultValue bool) bool {
+	defaultStr := "y/N"
+	if defaultValue {
+		defaultStr = "Y/n"
+	}
+
+	fmt.Printf("%s [%s]: ", prompt, defaultStr)
+	reader := bufio.NewReader(os.Stdin)
+	input, _ := reader.ReadString('\n')
+	input = strings.TrimSpace(strings.ToLower(input))
+
+	if input == "" {
+		return defaultValue
+	}
+
+	return input == "y" || input == "yes"
+}
+
+// PromptChoice prompts for a choice from a list
+func PromptChoice(prompt string, choices []string, defaultIndex int) int {
+	fmt.Println(prompt)
+	for i, choice := range choices {
+		marker := " "
+		if i == defaultIndex {
+			marker = "●"
+		} else {
+			marker = "○"
+		}
+		fmt.Printf("  %s %d. %s\n", marker, i+1, choice)
+	}
+	fmt.Println()
+	fmt.Printf("Choice [%d]: ", defaultIndex+1)
+
+	reader := bufio.NewReader(os.Stdin)
+	input, _ := reader.ReadString('\n')
+	input = strings.TrimSpace(input)
+
+	if input == "" {
+		return defaultIndex
+	}
+
+	choice, err := strconv.Atoi(input)
+	if err != nil || choice < 1 || choice > len(choices) {
+		fmt.Println("Invalid choice, using default")
+		return defaultIndex
+	}
+
+	return choice - 1
+}
+
+// GenerateRandomSecret generates a random hex string for JWT secrets
+func GenerateRandomSecret(bytes int) (string, error) {
+	b := make([]byte, bytes)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(b), nil
+}
+
+// PromptOrGenerate prompts for a value or generates one
+func PromptOrGenerate(prompt string, generator func() (string, error)) string {
+	fmt.Printf("%s (press Enter to generate): ", prompt)
+	reader := bufio.NewReader(os.Stdin)
+	input, _ := reader.ReadString('\n')
+	input = strings.TrimSpace(input)
+
+	if input == "" {
+		generated, err := generator()
+		if err != nil {
+			fmt.Printf("Error generating: %v\n", err)
+			return ""
+		}
+		fmt.Printf("Generated: %s\n", generated)
+		return generated
+	}
+
+	return input
+}
+
+// PrintHeader prints a formatted section header
+func PrintHeader(title string) {
+	fmt.Println()
+	fmt.Println(title)
+	fmt.Println(strings.Repeat("-", len(title)))
+}
+
+// PrintSuccess prints a success message
+func PrintSuccess(message string) {
+	fmt.Printf("✓ %s\n", message)
+}
+
+// PrintError prints an error message
+func PrintError(message string) {
+	fmt.Fprintf(os.Stderr, "✗ %s\n", message)
+}
+
+// PrintInfo prints an informational message
+func PrintInfo(message string) {
+	fmt.Printf("ℹ %s\n", message)
+}
+
+// Confirm asks for confirmation before proceeding
+func Confirm(prompt string) bool {
+	return PromptBool(prompt, false)
+}