fix: deduplicate entities by (title, type) in finalize_entities (#1718)

[HashwanthVen]

Summary

Fixes #1718.

finalize_entities deduplicated entity rows by title alone. When two
distinct entities share a title but have different types — for example IBM
extracted both as an ORGANIZATION and as a GEO, or the PARENT AREA case in
the original report — every row after the first for that title was silently
dropped, discarding its description and breaking the edges that referenced it.

This changes the dedup key to the (title, type) pair, so entities that are
genuinely distinct are preserved while true duplicates (same title and type)
are still collapsed to a single row.

Root cause

packages/graphrag/graphrag/index/operations/finalize_entities.py:

# before
if not title or title in seen_titles:
    continue
seen_titles.add(title)

seen_titles is keyed on title only, so the second (title, *) row of any
title is skipped regardless of its type.

Fix

# after
if not title:
    continue
key = (title, row.get("type"))
if key in seen_keys:
    continue
seen_keys.add(key)

The change is localized to the single dedup guard; degree lookup, id assignment,
human-readable id sequencing, and the output column projection are unchanged.

Tests

Added to tests/unit/indexing/test_finalize_graph.py::TestFinalizeEntities:

• test_keeps_same_title_different_type — two rows with the same title and
  different types are both written (the regression in [Fatal Bug]: Incorrect deduplication of entities with same title but different type #1718).
• test_deduplicates_same_title_and_type — true duplicates (same title and
  type) are still collapsed to one row.

The existing test_deduplicates_by_title continues to pass because its duplicate
rows share the default type, so they remain a true duplicate under the new key.

Run:

uv run poe test_unit -k TestFinalizeEntities

Notes

• Behavior is unchanged for the common single-type-per-title case.
• No schema, config, or storage-format changes; clean single-commit revert.
• A patch semversioner change document is included.

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