feat: payout gross-up (books.record_payout)

A platform deposit becomes a draft entry with the deposit, fees,
adjustments, and gross revenue (by class), refused unless gross - fees
+/- adjustments equals the deposit to the cent. The payout statement is
attached as its receipt before posting. 60 tools.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MtYEaR6M6Ybdhm6X98BWNu

crates/ledger-core/src/error.rs

@@ -137,6 +137,10 @@ pub enum LedgerError {
     #[error("invalid schedule: {0}")]
     InvalidSchedule(String),
 
+    /// A payout doesn't reconcile or uses the wrong accounts.
+    #[error("invalid payout: {0}")]
+    InvalidPayout(String),
+
     /// A tax category doesn't exist, doesn't fit the account, or has a bad
     /// deductible percent.
     #[error("invalid tax category: {0}")]