Modifier types: collapse or make load-bearing

# Context

`RequirementModifier.type` distinguishes `EXEMPTION` from `APPLICABILITY_CONDITION`. The compliance prompt and the LLM treat both identically: each short-circuits the evaluation to `NOT_APPLICABLE`. The legal distinction (an exemption waives an obligation that otherwise applies; an applicability condition gates whether the obligation reaches the product at all) is real but currently has no observable effect on the system's output. The two-type model adds curator effort and reviewer cognitive load with no payoff.

# Outcome

Either the modifier type is reduced to a single category, or the distinction between exemption and applicability condition produces a visible difference in the system's behaviour.

# Acceptance criteria

- The current modifier-type distinction either disappears from the schema, or is reflected in compliance output (verdict text, reason field, or downstream handling).
- Whichever path is taken, the rationale is documented so future curators understand which to use (or that there is no choice to make).
- Existing modifier rows migrate without changing the verdict produced for any current requirement.