Enhance contracts with driver authorization and platform fee management

[promisszn]

Summary

• Fleet owner authorization — added explicit caller parameter to add_driver_to_fleet with a code-level ownership check (matching the pattern already used by update_fleet_treasury), and added tests that confirm non-owners are rejected with Unauthorized
• Evidence hash — add_evidence_hash was already implemented; fixed a pre-existing test failure in resolve_dispute_refund_sender (mock delivery missing driver) and made the reputation penalty conditional so the dispute contract degrades gracefully when no identity contract is configured
• Slippage protection — execute_settlement_swap already enforced min_amount_out; added missing testutils dev-dependency that was causing compilation failure, introduced a mock router in tests, and added full slippage coverage for both same-asset and cross-asset paths
• Platform FX fee — added PlatformFeeBps storage key, set_platform_fee_bps (admin-only, capped at 10%) and get_platform_fee_bps functions; cross-asset swaps now route output through the contract before forwarding net amount to recipient; same-asset transfers deduct fee before sending; fee is collected by the admin address

Test results

130 tests across the workspace — 0 failures.

Closes #74
Closes #78
Closes #92
Closes #93

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