Fix/swap hardening

[sebas11042]

Summary

Hardens the in-contract swap path against fee-on-transfer inputs, stale/malformed paths, slippage edge cases, and protocol-fee accounting. Adds a dedicated swap hardening test suite and updates contract/shared error docs.

Type of change

• Bug fix
• New feature
• Documentation update
• Refactor / chore
• Smart contract change

Related issue

Closes #626

Changes

• Measure the actual amount received by the contract for swaps and compute output/protocol fee from that delta, protecting fee-on-transfer inputs.
• Reject malformed/stale swap paths, including repeated tokens, zero-liquidity hops, and insufficient output reserves.
• Refine exact-output swaps to respect max_amount_in under rounding and fee-on-transfer top-ups.
• Emit richer swap events with requested input, actual input, output, fee, and path length.
• Add tests/swap_hardening.rs with 19 tests covering fee-on-transfer, slippage, rounding, stale paths, rollback behavior, fee collector accounting, dust, and large values.
• Map swap-related ContractError codes in the shared error catalog and regenerate error-code docs.
• Update swap/contract documentation for measured inputs and hardened path behavior.

Testing

• Tested locally on Testnet
• Added/updated unit tests
• Manually tested UI flow

Local checks run:

cargo +stable fmt --check
cargo +stable clippy -- -D warnings
cargo +stable test
cargo +stable check --target wasm32v1-none
cargo +stable build --target wasm32v1-none --release
cargo audit
node scripts/generate-error-codes-doc.js --check
node smoke check for swap ContractError mappings

## Screenshots (if UI change)

<!-- Add before/after screenshots -->

## Checklist

- [x] My code follows the project style
- [x] I've updated docs if needed
- [x] No console errors or warnings
- [x] I've rebased on latest `main`

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