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>

tests/integration/test_landing_flow.py

@@ -0,0 +1,57 @@
+"""Integration test for complete landing page flow"""
+import pytest
+import os
+import yaml
+
+
+@pytest.fixture
+def test_product_for_flow(app):
+    """Create a test product for the integration flow"""
+    with app.app_context():
+        products_dir = os.path.join(app.config['DATA_DIR'], 'products')
+        product_dir = os.path.join(products_dir, 'flow-test-product')
+        os.makedirs(product_dir, exist_ok=True)
+
+        with open(os.path.join(product_dir, 'config.yaml'), 'w') as f:
+            yaml.dump({
+                'product_id': 'flow-test-product',
+                'name': 'Flow Test Product',
+                'submission_url_slug': 'flow-test-product',
+                'owner_language': 'en',
+                'assigned_owner_ids': [],
+                'status': 'active',
+                'description': 'Product for integration flow testing'
+            }, f)
+
+        yield 'flow-test-product'
+
+
+@pytest.mark.integration
+def test_landing_to_submission_flow(client, test_product_for_flow):
+    """T008: Complete flow - landing page → click product → submission form
+
+    Test the entire user journey:
+    1. User visits landing page
+    2. User sees products listed
+    3. User clicks on a product link
+    4. User is redirected to submission form for that product
+    """
+    # Step 1: Visit landing page
+    response = client.get('/')
+    assert response.status_code == 200
+
+    # Step 2: Verify product is listed
+    assert b'Flow Test Product' in response.data
+    assert b'flow-test-product' in response.data
+
+    # Step 3: Extract and verify product link
+    html = response.data.decode('utf-8')
+    assert '/submit/flow-test-product' in html, "Product link not found in landing page"
+
+    # Step 4: Click product link (navigate to submission form)
+    submission_response = client.get('/submit/flow-test-product')
+
+    # Should reach submission form (not 404)
+    assert submission_response.status_code == 200
+    # Should be on submission form page (has form or product name)
+    assert b'Flow Test Product' in submission_response.data or b'feedback' in submission_response.data.lower()