[did2 #6] ndi.document read-time augmentation with legacy aliases

[stevevanhooser]

Part of the NDI-matlab did2 migration. Target branch: Vnext.

Scope

When ndi.document materializes a V_delta doc (after the database layer's v1→V_delta normalization in issue 3), inject the legacy field aliases from ndi.compat.fieldAliases so customer code accessing doc.document_properties.probe_location.ontology_name (and the three other affected classes) still gets the right value.

• Walk the alias table from issue 5.
• For each row, copy the V_delta value into the legacy path.
• Mirror depends_on(k).value → depends_on(k).id for every entry.
• Idempotent: re-running on an already-augmented struct is a no-op.

Out of scope

• Write-back reconciliation — see issue 7.
• Query path translation — see issue 8.

Dependencies

• Issue 3 (database layer returns V_delta).
• Issue 5 (alias table).

[stevevanhooser]

Cleanup task added by PR #798 (route v1→V_delta normalisation through ndi.database):

When this issue lands, also remove the env-var gate that PR #798 introduced so the normalisation actually runs by default:

1. Delete the NDI_DID2_NORMALIZE_ON_READ gate in src/ndi/+ndi/+database/+internal/applyReadNormalization.m (the normalizationGateOn() helper and the if ~normalizationGateOn() block). The helper should always route the body through did2.convert.v1_to_v2 once the alias shim from this issue is in place.
2. Drop the OFF-state and gate-truthy/falsy tests from tests/+ndi/+unittest/+database/+internal/TestApplyReadNormalization.m (testGateOffWrapsBodyUnchanged, testGateTruthyValues, and the TestMethodSetup / TestMethodTeardown env-var save/restore plumbing).
3. Update the docstring on applyReadNormalization to drop the "gated by env var" paragraph.

Why the gate exists: with the converter active on every read but no compat alias shim in place, callers like ndi.database.fun.ndi_document2ndi_object (line 40, reads obj_struct.ndi_<parent>_class) and ndi.daq.metadatareader (writes daqmetadatareader.ndi_daqmetadatareader_class, then reconstructs via ndi_document2ndi_object) break — the converter renames the v1 field to its V_delta name (reader_class) and the v1 lookup misses. Issue #798 saw 44 unit-test failures from this exact pattern in test-vnext + run-tests before the gate was added. Once the alias table (issue 5 / #778, already merged) is wired up here, the gate becomes redundant.

Search anchor: grep -rn NDI_DID2_NORMALIZE_ON_READ src/ tests/ will surface every line to remove.

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