Draft: feat: add gift rating feature

Relates to issue #128

Changes

Gift Rating Feature Implementation

This merge request implements a complete gift rating system for the Present Picker application with the following key changes:

1. Rating State Management

• Added last_rating session state initialization in app.py (lines 44-45)
• Initializes to None to track when no rating has been given
• Follows existing session state pattern for consistency

2. Rating Box UI Component

• Created a 5-star rating interface below the chat interface (lines 85-97)
• Implemented using st.columns(5) for horizontal star button layout
• Each button displays ⭐ 1 through ⭐ 5 for intuitive user interaction
• Styled with dark theme background (rgba(47, 49, 54, 0.7)) matching the existing UI
• Button clicks store rating value and trigger rerun for immediate feedback

3. Confirmation Message Display

• Added confirmation message component (lines 99-106)
• Displays "✅ You rated this gift: X star(s). Thank you for your feedback!"
• Uses consistent dark background styling for visual cohesion
• Only appears after user selects a rating

Technical Details

• No new dependencies required - uses only Streamlit built-in components
• Rating persists in session state across reruns
• No changes needed to bot.py or other files
• Maintains existing chat functionality without breaking changes

Acceptance Criteria Met

• ✅ Users can see a rating box below the chat interface
• ✅ Users can select a rating from 1 to 5 stars
• ✅ App displays confirmation message with selected rating
• ✅ Rating box matches app's overall dark theme design
• ✅ Feature works without breaking existing chat functionality