Refactor Ledger PoV proof for new symmetric CERTS-pov (CIP-159)
After moving direct-deposit application from LEDGER-V into POST-CERT,
CERTS-pov now produces a symmetric "consumed = produced" equation:
getCoin s₁ + getCoin (DirectDepositsOf Γ)
≡ getCoin sₙ + getCoin (WithdrawalsOf Γ)
Thread the direct-deposit term through the LEDGER-pov proof:
* SUBLEDGERS-certs-pov gains "+ sum (map ddwl stxs)" on the LHS,
where ddwl = getCoin ∘ DirectDepositsOf is the per-sub-tx
direct-deposit total (analogous to wdrwl).
* combined-certs gains "+ allDirectDeps" on the LHS, composing the
per-sub CERTS-pov chain with the top-level call.
* The main LEDGER-V chain wraps the result in +-cancelʳ-≡ to
discharge the asymmetric "+ allDirectDeps" combined-certs introduces.
Removed:
* The certStateFinal local definition (LEDGER-V no longer applies
applyDirectDeposits).
* step-ii and the applyDirectDeposits-rewardsBalance module parameter
(subsumed by indexedSumᵛ'-∪⁺ inside POST-CERT-pov).
* The DD-split module parameter (subsumed by per-tx CERTS-pov chain).
* Stale "Key Lemma" subsection and stale commented-out lines in bat'.
* Unused imports +-identityʳ and +-0-monoid.
* Redundant local aliases in bat's where-block.
Documentation: rewrote "Key Differences from Conway" point 2 and the
LEDGER-V Proof Outline to reflect the new architecture; clarified the
LEDGER-I outline.