Feat/penalty fee distribution

[dumbdevss]

feat(contracts): route early-exit penalty fees to the lending pool as yield

Closes #179

Early-withdrawal penalties were left idle in the escrow contract. They now flow
to the LendingPool and are distributed to active investors as yield.

Changes

• lending-pool: new deposit_fees(from, amount) — pulls the fee tokens and
  books them as claimable liquidity plus pro-rata yield by incrementing the
  total-repaid-interest accumulator, the same mechanism used for loan-interest
  repayments. So every depositor's claim_yield rises in proportion to their
  share.
• escrow: admin-only set_lending_pool / get_lending_pool. withdraw now
  forwards the penalty to the configured pool via deposit_fees, authorizing the
  nested token.transfer as the invoking contract
  (authorize_as_current_contract). With no pool configured, behavior is
  unchanged (penalty stays in escrow).
• Fixes a pre-existing missing PoolError::LoanNotOverdue variant that prevented
  the lending-pool crate from compiling.

Tests

• New end-to-end escrow↔pool test
  (test_early_withdrawal_penalty_routes_to_lending_pool): after an early exit,
  pool TVL and the sole investor's claimable yield both rise by exactly the
  penalty.
• Full escrow suite green (52 passed).

Acceptance criteria

• Escrow withdrawal penalties transfer to the lending pool
• Yield increments distributed proportionally across active depositors
• End-to-end integration test passes

Note: the lending-pool's own src/test.rs is a pre-existing broken stub
(placeholder comments, ~76 compile errors on main) and is out of scope here;
the new behavior is verified through the escrow integration test against the
real pool.

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