Define StageBridge model output contract

[SecondBook5]

Purpose

StageBridge needs a strict, versioned model output contract so every valid model run produces the same core artifacts, columns, metadata, and validation checks. The model output should not be an informal collection of latent arrays, plots, or notebook objects. It should be a structured receiver-level transition report with companion counterfactual, region-level, vector-field, and run-manifest outputs.

This issue defines the required output contract for stagebridge-core.

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Core

[SecondBook5]

Stage ontology correction for the StageBridge output/model contract:

For LUAD v1, MIA and LUAD should be merged into a single invasive stage because MIA is too sparse to support a stable standalone stage bank.

Canonical LUAD v1 stage ontology:

Normal -> AAH -> AIS -> Invasive

Canonical LUAD v1 stage edges:

normal__to__aah
aah__to__ais
ais__to__invasive

Do not implement mia__to__luad as a required v1 edge. MIA and LUAD may be retained in metadata as stage_fine, but the model-facing stage_model should map both