VectorMatch.entry_id renamed to VectorMatch.id to match the API contract
expected by downstream consumers (pagepiper T7). The dataclass remains frozen
to prevent field reassignment; metadata is kept as plain dict for JSON
deserialization compatibility.
- Renamed VectorMatch.entry_id field to id
- Updated all test references to use .id accessor
- Simplified metadata to plain dict (removed MappingProxyType wrapping)
- All 7 tests passing
