Persist typed vector graph edges

[SWORDIntel]

What changed

• persist typed relation edges in a versioned, checksummed CSR container section separate from HNSW
• replay add, replace, and remove mutations through the WAL and checkpoint them atomically
• validate endpoints, make duplicate additions idempotent, and add batch, typed-neighbor, metadata, replacement, and removal APIs
• preserve the existing add_edge and get_edges ABI and load older containers without an edge section as empty

Why

The prior explicit-edge API reported successful writes while keeping relationships only in process memory, so edges disappeared after reopen and could not support qlearn context graph traversal.

Validation

• make test-edge-persistence QIHSE_ENABLE_AVX512=0 QIHSE_ENABLE_AMX=0 QIHSE_ENABLE_AVX_VNNI=0
• python3 tests/test_python_edges.py -v
• full lib-ctypes build
• exported-symbol inspection for legacy and additive edge APIs

The pre-existing general persistence test currently does not compile because its test source dereferences an opaque database handle and references a removed stats field; this branch does not modify that unrelated test.