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/app/routes/assistant.py

@@ -0,0 +1,84 @@
+"""Site assistant routes — global AI helper for the product UI."""
+import json
+
+from flask import Blueprint, Response, jsonify, request, stream_with_context
+
+from app.extensions import limiter
+from app.services.policy_service import resolve_web_actor
+from app.services.site_assistant_service import chat_with_site_assistant, stream_site_assistant_chat
+
+assistant_bp = Blueprint("assistant", __name__)
+
+
+def _parse_chat_payload():
+    payload = request.get_json(silent=True) or {}
+
+    message = str(payload.get("message", "")).strip()
+    if not message:
+        return None, (jsonify({"error": "Message is required."}), 400)
+
+    if len(message) > 4000:
+        return None, (jsonify({"error": "Message is too long."}), 400)
+
+    actor = resolve_web_actor()
+    return {
+        "message": message,
+        "session_id": str(payload.get("session_id", "")).strip() or None,
+        "fingerprint": str(payload.get("fingerprint", "")).strip() or "anonymous",
+        "tool_slug": str(payload.get("tool_slug", "")).strip(),
+        "page_url": str(payload.get("page_url", "")).strip(),
+        "locale": str(payload.get("locale", "en")).strip() or "en",
+        "user_id": actor.user_id,
+        "history": payload.get("history") if isinstance(payload.get("history"), list) else None,
+    }, None
+
+
+def _sse(event: str, data: dict) -> str:
+    return f"event: {event}\ndata: {json.dumps(data, ensure_ascii=True)}\n\n"
+
+
+@assistant_bp.route("/chat", methods=["POST"])
+@limiter.limit("20/minute")
+def assistant_chat_route():
+    """Answer a product-help message and store the conversation for later analysis."""
+    chat_kwargs, error_response = _parse_chat_payload()
+    if error_response:
+        return error_response
+
+    try:
+        result = chat_with_site_assistant(**chat_kwargs)
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 400
+    except Exception:
+        return jsonify({"error": "Assistant is temporarily unavailable."}), 500
+
+    return jsonify(result), 200
+
+
+@assistant_bp.route("/chat/stream", methods=["POST"])
+@limiter.limit("20/minute")
+def assistant_chat_stream_route():
+    """Stream assistant replies incrementally over SSE."""
+    chat_kwargs, error_response = _parse_chat_payload()
+    if error_response:
+        return error_response
+
+    try:
+        events = stream_site_assistant_chat(**chat_kwargs)
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 400
+    except Exception:
+        return jsonify({"error": "Assistant is temporarily unavailable."}), 500
+
+    def generate():
+        for event in events:
+            yield _sse(event["event"], event["data"])
+
+    return Response(
+        stream_with_context(generate()),
+        content_type="text/event-stream; charset=utf-8",
+        headers={
+            "Cache-Control": "no-cache",
+            "X-Accel-Buffering": "no",
+        },
+    )