fix(strategies): remove IRON_BUTTERFLY enum alias that shadowed BUTTERFLY (#4)

[bradsmithmba]

Summary

StrategyType defined two members with the same value:

BUTTERFLY = "butterfly"
IRON_BUTTERFLY = "butterfly"

In Python, identical enum values make the second member a silent alias of the first:

>>> StrategyType.IRON_BUTTERFLY is StrategyType.BUTTERFLY
True
>>> {StrategyType.BUTTERFLY: 'a', StrategyType.IRON_BUTTERFLY: 'b'}
{<StrategyType.BUTTERFLY: 'butterfly'>: 'b'}   # one key, 'a' silently dropped

Any code that used both as distinct dictionary keys (probabilities, risk metrics, score maps) would silently lose one entry.

Closes #4.

Why remove rather than make distinct

The codebase canonically identifies the iron butterfly as BUTTERFLY:

• IronButterflyStrategy.get_strategy_type() returns StrategyType.BUTTERFLY
• the factory registry maps StrategyType.BUTTERFLY -> IronButterflyStrategy
• regime mappings, recommendation_engine, the API layer, and the curriculum all key on BUTTERFLY
• there is only one butterfly-family implementation

IRON_BUTTERFLY was referenced in exactly one place: tests/models/test_scoring_engine.py. Making it a distinct value would create an orphan enum member with no implementation and no factory mapping. Removing the redundant alias and pointing that test at the canonical BUTTERFLY is the minimal correct fix.

Changes

• src/strategies/base.py: remove IRON_BUTTERFLY = "butterfly"; add a comment explaining BUTTERFLY is the canonical iron-butterfly member.
• tests/models/test_scoring_engine.py: StrategyType.IRON_BUTTERFLY -> StrategyType.BUTTERFLY (3 references).

Verification

StrategyType has IRON_BUTTERFLY:  False
StrategyType member count:        16   (unchanged — the alias was never a distinct member)

$ pytest tests/models/test_scoring_engine.py tests/strategies/ -q
149 passed

Note

The naming is still imperfect — BUTTERFLY represents an iron butterfly. Renaming BUTTERFLY -> IRON_BUTTERFLY across the ~30 references in 10+ files would better reflect the implementation, but that is a larger refactor and out of scope for this fix.

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