feat: Add Piper voice download helpers and guides

- Created download_piper_voices.py for automated download attempts
- Created download_piper_voices.sh as alternative bash script
- Created EASY_PIPER_SETUP.md with simple 3-step instructions
- Created PIPER_DOWNLOAD_GUIDE.md with visual step-by-step guide
- Includes troubleshooting, checklists, and pro tips

Makes Piper setup much easier for users with multiple guide options.

backend/download_piper_voices.sh

@@ -0,0 +1,149 @@
+#!/bin/bash
+# Helper script to download Piper TTS voice models
+
+set -e
+
+echo "=================================================="
+echo "Piper TTS Voice Model Downloader"
+echo "=================================================="
+echo ""
+
+# Create models directory
+MODELS_DIR="$(dirname "$0")/piper_models"
+mkdir -p "$MODELS_DIR"
+echo "✓ Models directory: $MODELS_DIR"
+echo ""
+
+# Base URL for Piper voices
+BASE_URL="https://huggingface.co/rhasspy/piper-voices/resolve/main"
+
+# Function to download a voice
+download_voice() {
+    local voice_id=$1
+    local lang_code=$2
+    
+    echo "Downloading $voice_id..."
+    
+    # Construct URLs
+    local model_url="${BASE_URL}/${lang_code}/${lang_code}_${voice_id}.onnx"
+    local config_url="${BASE_URL}/${lang_code}/${lang_code}_${voice_id}.onnx.json"
+    
+    local model_file="${MODELS_DIR}/${lang_code}-${voice_id}.onnx"
+    local config_file="${MODELS_DIR}/${lang_code}-${voice_id}.onnx.json"
+    
+    # Check if already exists
+    if [ -f "$model_file" ] && [ -f "$config_file" ]; then
+        echo "  ✓ Already downloaded"
+        return 0
+    fi
+    
+    # Download with curl
+    if command -v curl &> /dev/null; then
+        echo "  Downloading model file..."
+        curl -L -o "$model_file" "$model_url" 2>/dev/null || {
+            echo "  ✗ Failed to download model"
+            return 1
+        }
+        
+        echo "  Downloading config file..."
+        curl -L -o "$config_file" "$config_url" 2>/dev/null || {
+            echo "  ✗ Failed to download config"
+            return 1
+        }
+        
+        # Verify files are not error pages
+        if [ $(wc -c < "$model_file") -lt 1000 ]; then
+            echo "  ✗ Download failed (file too small)"
+            rm -f "$model_file" "$config_file"
+            return 1
+        fi
+        
+        echo "  ✓ Downloaded successfully"
+        return 0
+    else
+        echo "  ✗ curl not found"
+        return 1
+    fi
+}
+
+echo "Select voices to download:"
+echo ""
+echo "Recommended starter pack (3 voices):"
+echo "  1) en_US-lessac-medium (Male, American)"
+echo "  2) en_US-amy-medium (Female, American)"
+echo "  3) en_GB-alan-medium (Male, British)"
+echo ""
+echo "All English voices (5 voices):"
+echo "  4) All of the above + 2 more"
+echo ""
+echo "Manual selection:"
+echo "  5) Choose specific voices"
+echo ""
+echo "  0) Exit"
+echo ""
+read -p "Enter your choice (0-5): " choice
+
+case $choice in
+    1)
+        echo ""
+        echo "Downloading starter pack..."
+        echo ""
+        download_voice "lessac-medium" "en_US"
+        download_voice "amy-medium" "en_US"
+        download_voice "alan-medium" "en_GB"
+        ;;
+    2)
+        echo ""
+        echo "Downloading all English voices..."
+        echo ""
+        download_voice "lessac-medium" "en_US"
+        download_voice "amy-medium" "en_US"
+        download_voice "libritts-high" "en_US"
+        download_voice "alan-medium" "en_GB"
+        download_voice "alba-medium" "en_GB"
+        ;;
+    3)
+        echo ""
+        echo "Available voices:"
+        echo "  en_US-lessac-medium (Male, American)"
+        echo "  en_US-amy-medium (Female, American)"
+        echo "  en_US-libritts-high (Neutral, American, High Quality)"
+        echo "  en_GB-alan-medium (Male, British)"
+        echo "  en_GB-alba-medium (Female, British)"
+        echo ""
+        echo "Enter voice IDs separated by spaces (e.g., lessac-medium amy-medium):"
+        read -p "> " voices
+        
+        for voice in $voices; do
+            if [[ $voice == *"GB"* ]]; then
+                download_voice "$voice" "en_GB"
+            else
+                download_voice "$voice" "en_US"
+            fi
+        done
+        ;;
+    0)
+        echo "Exiting..."
+        exit 0
+        ;;
+    *)
+        echo "Invalid choice"
+        exit 1
+        ;;
+esac
+
+echo ""
+echo "=================================================="
+echo "Download Summary"
+echo "=================================================="
+echo ""
+echo "Downloaded files in: $MODELS_DIR"
+ls -lh "$MODELS_DIR" 2>/dev/null || echo "No files found"
+echo ""
+echo "✓ Setup complete!"
+echo ""
+echo "Next steps:"
+echo "  1. Test Piper: python test_piper_direct.py"
+echo "  2. Start backend: uvicorn main:app --reload"
+echo "  3. Select 'Piper TTS' in the UI"
+echo ""