feat: enhance installer script for existing installation support

- Add automatic detection of existing installations via .env file
- Load and display existing configuration with masked API key for security
- Prompt user to keep existing configuration or update with new values
- Use existing values as defaults when prompting for configuration changes
- Handle API key updates with option to keep current or enter new one
- Detect running services and restart instead of start for existing installations
- Display context-appropriate success messages (Update vs Installation completed)
- Show correct access URLs based on configured host (localhost for 0.0.0.0)

User Experience Improvements:
- Skip configuration prompts entirely if user chooses to keep existing config
- Show current values as defaults in all configuration prompts
- Provide clear feedback about existing vs fresh installation flows
- Intelligently handle service management for updates vs new installs

Example flow for existing installation:
1. Detect existing .env file
2. Load and display current configuration (API key masked)
3. Ask: "Do you want to keep the existing configuration? [Y/n]"
4. If Yes: Use existing config, skip prompts
5. If No: Prompt with current values as defaults
6. Restart service if running, start if stopped
7. Display "Update completed successfully!"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

scripts/install.sh

@@ -25,34 +25,115 @@ echo "Installation directory: $INSTALL_DIR"
 echo "Service name: $SERVICE_NAME"
 echo ""
 
-# Prompt for API key
-echo "Please enter the API key for authentication:"
-read -s API_KEY
-echo ""
-
-if [ -z "$API_KEY" ]; then
-    echo "Error: API key cannot be empty"
-    exit 1
+# Check if application is already installed
+EXISTING_INSTALLATION=false
+EXISTING_ENV_FILE="$INSTALL_DIR/.env"
+
+if [ -f "$EXISTING_ENV_FILE" ]; then
+    EXISTING_INSTALLATION=true
+    echo "Existing installation detected!"
+    echo "Found existing configuration at: $EXISTING_ENV_FILE"
+    echo ""
+
+    # Load existing configuration
+    source "$EXISTING_ENV_FILE" 2>/dev/null || true
+
+    # Set defaults from existing config or fallback to hardcoded defaults
+    EXISTING_API_KEY="$API_KEY"
+    EXISTING_HOST="${HOST:-0.0.0.0}"
+    EXISTING_PORT="${PORT:-3000}"
+    EXISTING_MAX_CONCURRENT_JOBS="${MAX_CONCURRENT_JOBS:-3}"
+
+    echo "Current configuration:"
+    echo "  API Key: ${EXISTING_API_KEY:0:8}... (masked)"
+    echo "  Host: $EXISTING_HOST"
+    echo "  Port: $EXISTING_PORT"
+    echo "  Max Concurrent Jobs: $EXISTING_MAX_CONCURRENT_JOBS"
+    echo ""
+
+    # Ask if user wants to keep existing configuration
+    echo "Do you want to keep the existing configuration? [Y/n]:"
+    read KEEP_CONFIG
+    KEEP_CONFIG=${KEEP_CONFIG:-Y}
+
+    if [[ "$KEEP_CONFIG" =~ ^[Yy]([Ee][Ss])?$ ]]; then
+        echo "Using existing configuration..."
+        API_KEY="$EXISTING_API_KEY"
+        HOST="$EXISTING_HOST"
+        PORT="$EXISTING_PORT"
+        MAX_CONCURRENT_JOBS="$EXISTING_MAX_CONCURRENT_JOBS"
+        SKIP_CONFIG_PROMPTS=true
+    else
+        echo "Will prompt for new configuration..."
+        SKIP_CONFIG_PROMPTS=false
+    fi
+    echo ""
+else
+    echo "No existing installation found. Starting fresh installation..."
+    echo ""
+    SKIP_CONFIG_PROMPTS=false
 fi
 
-# Prompt for host/IP address
-echo "Enter the host/IP address to listen on:"
-echo "  - 0.0.0.0 for all interfaces (accessible from anywhere)"
-echo "  - 127.0.0.1 for localhost only (accessible only from this machine)"
-echo "  - or enter a specific IP address"
-echo "Default: 0.0.0.0"
-read HOST
-HOST=${HOST:-0.0.0.0}
-
-# Prompt for port (optional)
-echo "Enter the HTTP port (default: 3000):"
-read PORT
-PORT=${PORT:-3000}
-
-# Prompt for max concurrent jobs (optional)
-echo "Enter the maximum number of concurrent jobs (default: 3):"
-read MAX_CONCURRENT_JOBS
-MAX_CONCURRENT_JOBS=${MAX_CONCURRENT_JOBS:-3}
+# Configuration prompts (skip if using existing config)
+if [ "$SKIP_CONFIG_PROMPTS" != "true" ]; then
+    # Prompt for API key
+    if [ "$EXISTING_INSTALLATION" = "true" ]; then
+        echo "Enter new API key for authentication (current: ${EXISTING_API_KEY:0:8}...):"
+        echo "Press Enter to keep current API key, or enter new one:"
+        read -s NEW_API_KEY
+        if [ -n "$NEW_API_KEY" ]; then
+            API_KEY="$NEW_API_KEY"
+        else
+            API_KEY="$EXISTING_API_KEY"
+        fi
+    else
+        echo "Please enter the API key for authentication:"
+        read -s API_KEY
+    fi
+    echo ""
+
+    if [ -z "$API_KEY" ]; then
+        echo "Error: API key cannot be empty"
+        exit 1
+    fi
+
+    # Prompt for host/IP address
+    echo "Enter the host/IP address to listen on:"
+    echo "  - 0.0.0.0 for all interfaces (accessible from anywhere)"
+    echo "  - 127.0.0.1 for localhost only (accessible only from this machine)"
+    echo "  - or enter a specific IP address"
+    if [ "$EXISTING_INSTALLATION" = "true" ]; then
+        echo "Current: $EXISTING_HOST, Default: $EXISTING_HOST"
+        read HOST
+        HOST=${HOST:-$EXISTING_HOST}
+    else
+        echo "Default: 0.0.0.0"
+        read HOST
+        HOST=${HOST:-0.0.0.0}
+    fi
+
+    # Prompt for port (optional)
+    if [ "$EXISTING_INSTALLATION" = "true" ]; then
+        echo "Enter the HTTP port (current: $EXISTING_PORT):"
+        read PORT
+        PORT=${PORT:-$EXISTING_PORT}
+    else
+        echo "Enter the HTTP port (default: 3000):"
+        read PORT
+        PORT=${PORT:-3000}
+    fi
+
+    # Prompt for max concurrent jobs (optional)
+    if [ "$EXISTING_INSTALLATION" = "true" ]; then
+        echo "Enter the maximum number of concurrent jobs (current: $EXISTING_MAX_CONCURRENT_JOBS):"
+        read MAX_CONCURRENT_JOBS
+        MAX_CONCURRENT_JOBS=${MAX_CONCURRENT_JOBS:-$EXISTING_MAX_CONCURRENT_JOBS}
+    else
+        echo "Enter the maximum number of concurrent jobs (default: 3):"
+        read MAX_CONCURRENT_JOBS
+        MAX_CONCURRENT_JOBS=${MAX_CONCURRENT_JOBS:-3}
+    fi
+fi
 
 echo ""
 echo "Configuration:"
@@ -161,14 +242,30 @@ systemctl daemon-reload
 echo "Enabling service..."
 systemctl enable "$SERVICE_NAME"
 
-# Start service
-echo "Starting service..."
-systemctl start "$SERVICE_NAME"
+# Handle service startup based on existing installation
+if [ "$EXISTING_INSTALLATION" = "true" ]; then
+    # Check if service is already running
+    if systemctl is-active --quiet "$SERVICE_NAME"; then
+        echo "Service is currently running. Restarting with new configuration..."
+        systemctl restart "$SERVICE_NAME"
+    else
+        echo "Starting service..."
+        systemctl start "$SERVICE_NAME"
+    fi
+else
+    # Fresh installation - start service
+    echo "Starting service..."
+    systemctl start "$SERVICE_NAME"
+fi
 
 # Check status
 echo ""
 echo "==================================="
-echo "Installation completed successfully!"
+if [ "$EXISTING_INSTALLATION" = "true" ]; then
+    echo "Update completed successfully!"
+else
+    echo "Installation completed successfully!"
+fi
 echo "==================================="
 echo ""
 echo "Service status:"
@@ -181,6 +278,13 @@ echo "  Restart service: sudo systemctl restart $SERVICE_NAME"
 echo "  View logs:       sudo journalctl -u $SERVICE_NAME -f"
 echo "  Check status:    sudo systemctl status $SERVICE_NAME"
 echo ""
-echo "API is available at: http://localhost:$PORT"
-echo "Health check: http://localhost:$PORT/health"
+# Display appropriate URL based on host configuration
+if [ "$HOST" = "0.0.0.0" ]; then
+    DISPLAY_HOST="localhost"
+else
+    DISPLAY_HOST="$HOST"
+fi
+
+echo "API is available at: http://$DISPLAY_HOST:$PORT"
+echo "Health check: http://$DISPLAY_HOST:$PORT/health"
 echo ""