feat(rebalancer): add Katana external bridge

[Mo-Hussain]

Summary

• add a Katana IExternalBridge for the public LayerZero composer path
• support exact-in ethereum USDC -> katana vbUSDC and katana vbUSDC -> ethereum USDC
• materialize exact calldata from live previewDeposit / previewRedeem and quoteSend, following the private-agents#53 path builder pattern
• wire the new bridge into rebalancer config/factory and add focused builder/bridge/config tests

Testing

• pnpm -C typescript/rebalancer exec mocha --config .mocharc.json './src/bridges/katanaUtils.test.ts' './src/bridges/KatanaBridge.test.ts' './src/config/RebalancerConfig.test.ts' --exit

Notes

• pnpm -C typescript/rebalancer build is currently blocked by unrelated pre-existing type errors in src/interfaces/IRebalancer.ts, src/strategy/MinAmountStrategy.ts, src/test/helpers.ts, and src/utils/balanceUtils.ts