Implement product selection landing page (Feature 002)

Adds landing page at root URL (/) that displays all active products with links to feedback submission forms. This replaces the requirement for users to know direct product URLs.

Changes:
- Added Product.load_active() method to filter and sort active products alphabetically
- Created landing route blueprint with error handling and structured logging
- Registered landing blueprint in app factory, replacing old index route
- Created landing page template with product list and empty state
- Added comprehensive contract tests (6 tests) covering active products, filtering, sorting, XSS prevention
- Added integration test for complete user flow from landing page to submission form

All 7 tests pass. User Story 1 (P1 - MVP) complete.

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

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

app/routes/landing.py

@@ -0,0 +1,29 @@
+"""Landing page route - product selection"""
+from flask import Blueprint, render_template, current_app
+from app.models.product import Product
+
+landing_bp = Blueprint('landing', __name__)
+
+
+@landing_bp.route('/')
+def index():
+    """Landing page showing all active products for feedback submission
+
+    Returns:
+        Rendered HTML template with:
+        - List of active products (if any)
+        - Empty state message (if no active products)
+    """
+    try:
+        products = Product.load_active()
+        current_app.logger.info(
+            f'Landing page accessed: {len(products)} active products available'
+        )
+        return render_template('landing/index.html', products=products)
+    except Exception as e:
+        current_app.logger.error(
+            f'Error loading landing page: {e}',
+            exc_info=True
+        )
+        # Graceful degradation - show empty product list
+        return render_template('landing/index.html', products=[])