[JingsongLi]

Purpose

Remove native Lumina vector-index support and recommend vindex DiskANN for vector search.

Related: #227.

Brief change log

• Delete the Lumina FFI, reader, index builder, and backend dispatch branches.
• Remove the Lumina index identifiers and sys.create_lumina_index procedure, with regression tests for the removed entry points.
• Migrate shared search tests to vindex, replace the native-library E2E test with a regular DiskANN build/query test, and remove the Lumina fixture and CI installation steps.

Tests

• cargo test --locked -p paimon --lib --features fulltext: 4,616 passed, 6 ignored.
• cargo test --locked -p paimon --test pk_vector_baseline_test --features fulltext: 8 passed.
• TZ=UTC cargo test --locked -p paimon-datafusion --test procedures --features fulltext: 64 passed.
• cargo test --locked -p paimon-datafusion --test read_tables --features fulltext vector_search_tests: 12 passed, including the DiskANN build/query E2E test.
• cargo fmt --all -- --check and git diff --check passed.

The full DataFusion library run had 355 passing tests and 7 failures with TableNotExist for unavailable local partition-table fixtures (partitioned_log_table and multi_partitioned_log_table). The procedure suite requires TZ=UTC for its existing timestamp-based tests.

API and Format

Remove the public paimon::lumina module, sys.create_lumina_index, and the lumina / lumina-vector-ann index identifiers. Existing Lumina indexes must be rebuilt in the vindex format; build DiskANN indexes through sys.create_global_index with index_type => 'diskann'.

Documentation

Update the SQL guide to recommend vindex DiskANN and remove Lumina options and native-library setup instructions. Add a migration note to the upcoming release while preserving historical release entries.

[leaves12138]

LGTM