feat: add site assistant component for guided tool selection

- Introduced SiteAssistant component to assist users in selecting the right tools based on their queries.
- Integrated assistant into the main App component.
- Implemented message handling and storage for user-assistant interactions.
- Added quick prompts for common user queries related to tools.
- Enhanced ToolLandingPage and DownloadButton components with SharePanel for sharing tool results.
- Updated translations for new assistant features and sharing options.
- Added API methods for chat functionality with the assistant, including streaming responses.

backend/tests/test_assistant.py

@@ -0,0 +1,71 @@
+"""Tests for the site assistant API route."""
+
+import json
+
+
+class TestAssistantRoute:
+    def test_requires_message(self, client):
+        response = client.post('/api/assistant/chat', json={})
+        assert response.status_code == 400
+        assert response.get_json()['error'] == 'Message is required.'
+
+    def test_success_returns_reply_and_session(self, client, monkeypatch):
+        monkeypatch.setattr(
+            'app.routes.assistant.chat_with_site_assistant',
+            lambda **kwargs: {
+                'session_id': kwargs['session_id'] or 'assistant-session-1',
+                'reply': 'Use Merge PDF for combining files.',
+                'stored': True,
+            },
+        )
+
+        response = client.post(
+            '/api/assistant/chat',
+            json={
+                'message': 'How do I combine files?',
+                'fingerprint': 'visitor-1',
+                'tool_slug': 'merge-pdf',
+            },
+        )
+
+        assert response.status_code == 200
+        body = response.get_json()
+        assert body['stored'] is True
+        assert body['reply'] == 'Use Merge PDF for combining files.'
+        assert body['session_id']
+
+    def test_stream_returns_sse_events(self, client, monkeypatch):
+        monkeypatch.setattr(
+            'app.routes.assistant.stream_site_assistant_chat',
+            lambda **kwargs: iter([
+                {'event': 'session', 'data': {'session_id': 'assistant-session-1'}},
+                {'event': 'chunk', 'data': {'content': 'Use Merge '}},
+                {'event': 'chunk', 'data': {'content': 'PDF.'}},
+                {
+                    'event': 'done',
+                    'data': {
+                        'session_id': 'assistant-session-1',
+                        'reply': 'Use Merge PDF.',
+                        'stored': True,
+                    },
+                },
+            ]),
+        )
+
+        response = client.post(
+            '/api/assistant/chat/stream',
+            json={
+                'message': 'How do I combine files?',
+                'fingerprint': 'visitor-1',
+                'tool_slug': 'merge-pdf',
+            },
+        )
+
+        assert response.status_code == 200
+        assert response.headers['Content-Type'].startswith('text/event-stream')
+
+        body = response.get_data(as_text=True)
+        assert 'event: session' in body
+        assert f"data: {json.dumps({'session_id': 'assistant-session-1'})}" in body
+        assert 'event: chunk' in body
+        assert 'Use Merge PDF.' in body