UPLC: handle JS boolean in the Bool constant encoder

## Summary
The flat encoder for a Bool constant reads value.index, but ConstantValue also permits a plain JS boolean. A JS false has no .index, so (false).index === 0n is false and the encoder emits the True bit. con bool false and con bool true then produce identical flat bytes, so a script built from a false boolean computes that constant as true. Narrow in practice (parameter application uses con data, never con bool), but the public type invites the call that triggers it.

## Affected
packages/evolution/src/UPLC.ts Bool encoder (L954)
packages/evolution/src/UPLC.ts ConstantValue type (L194), constantTerm (L1282)
decoder representation: UPLC.ts (L660)

## Fix
Handle the primitive form the type advertises in the encoder, e.g.
const bit = typeof value === "boolean" ? (value ? 1 : 0) : (value.index === 0n ? 0 : 1)
Or drop boolean from ConstantValue so { index } is the only representation and the footgun cannot typecheck.

## Regression test
- given: a program whose body is constantTerm("Bool", false)
- before fix: flat(con bool false) === flat(con bool true), and decoding flat(con bool false) yields index 1 (True)
- after fix: flat(con bool false) !== flat(con bool true), and decoding flat(con bool false) yields index 0 (False)

Must FAIL on main today and PASS after the fix.

## Reference
Report 11

packages/evolution/src/UPLC.ts の L954 付近にある Bool エンコーダーから始め、次に L194 と L1282 付近の ConstantValue および constantTerm の定義と、L660 付近のデコーダーを読みます。Issue で説明されているリグレッションカバレッジを追加し、false と true が異なる flat バイト列を生成し、false がインデックス 0 にデコードされることを確認します。

索引モデルが issue の本文から書いたものです。