[BUG] Semantic-guided read paths read chunk.value directly and break under an external ChunkStore

**Package version:** 3.18.5
**Package:** lexical-graph
**Python version:** 3.12
**OS:** Linux

## Description

#437 moved the traversal-based read paths onto `ChunkStore`. The semantic-guided stack still reads `chunk.value` off the graph, so it breaks once a deployment configures an external chunk store and `ChunkGraphBuilder` stops writing that property (`indexing/build/chunk_graph_builder.py:80-88`).

Two queries fetch chunk nodes with no property list, which defaults to `['*']` (`storage/graph/graph_utils.py:130`) and drags the full text back on every call:

- `retrieval/utils/chunk_utils.py:60` — `get_chunks_query`
- `retrieval/utils/statement_utils.py:124` — `get_statements_query`

Three consumers index `['value']` on the result and raise `KeyError` once the property is gone:

- `retrieval/retrievers/deprecated/semantic_guided_chunk_retriever.py:173`
- `retrieval/retrievers/deprecated/semantic_guided_retriever.py:218`
- `retrieval/post_processors/statement_enhancement.py:103`, which feeds that text to the LLM as synthesis context

`StatementEnhancementPostProcessor` is not deprecated, and it ships in the docs, an example notebook, and the integration tests.

#437 skipped `get_chunks_query` on purpose: "left as-is since its only caller is deprecated." That held while the property was still written.

## Steps to reproduce

Needs the S3 backend from #465. `InGraphChunkStore` is the only store on `main` and it still writes `chunk.value`.

Set `GraphRAGConfig.s3_chunk_store`, index a document set, then query through `SemanticGuidedRetriever` — with `StatementEnhancementPostProcessor` enabled, or with a chunk retriever. Both hit `KeyError: 'value'`.

## Expected

The semantic-guided paths resolve chunk text through `ChunkStore`, the way `keyword_vss_provider.py` and `traversal_based_base_retriever.py` do.

## Proposed fix

- Wire `statement_enhancement.py` to `ChunkStore`.
- Wire the semantic-guided retrievers, or delete them along with `get_chunks_query`, which has no other caller.
- Name the properties in whichever `node_result` calls survive, so these queries stop pulling text they may not use.

This should land before an external chunk store becomes the default.