fix: align LLMSummarizer output_types key with actual return key

[rekha0suthar]

Related Issues

Fixes #490

Proposed Changes

LLMSummarizer.run() declared its output type as summary via @component.output_types(summary=list[Document]), but actually returned {"documents": documents}. This key mismatch means any pipeline connecting to llm_summarizer.summary would fail at runtime, because the declared output edge does not exist.

Changed the decorator to @component.output_types(documents=list[Document]) so the declared output key matches the actual return key "documents", consistent with:

• The existing unit and integration tests (which already assert on result["documents"]).
• The convention used by other document-processing components in Haystack (returning enriched documents under the documents key).

How to test

from unittest.mock import Mock
from haystack import Document
from haystack.dataclasses import ChatMessage
from haystack_experimental.components.summarizers.llm_summarizer import LLMSummarizer

mock_generator = Mock()
mock_generator.run = Mock(return_value={"replies": [ChatMessage.from_assistant("Short summary.")]})

summarizer = LLMSummarizer(chat_generator=mock_generator)
summarizer._document_splitter._is_warmed_up = True

result = summarizer.run(documents=[Document(content="A long text to summarize.")])
assert "documents" in result  # was KeyError before the fix

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