feat(contracts): Lithoswap V2 DEX for Makalu (item 1 native swap venue)

[bachal-mb]

feat(contracts): Lithoswap V2 DEX for Makalu (item 1 — native swap venue)

Adds the on-chain venue for the MultX cross-chain token swap: a Uniswap V2
port on solc 0.8.24 under Makalu/contracts/src/dex/ (Factory, Pair, Router02,
LP ERC20, libraries, interfaces).

Design choices for Makalu:

• Router resolves pairs via factory.getPair() rather than a hardcoded CREATE2
  init-code hash. Under via_ir/0.8.24 the Pair bytecode hash differs from the
  canonical Uniswap value, so the hardcoded-hash approach silently breaks
  ("router can't find the pair"); getPair avoids that entire class of bug.
• Router is ERC20<->ERC20 only (no payable/native paths). On Makalu the native
  LITHO is a LEP-100 token that WLITHO already wraps as an ERC20, so every swap
  is token-to-token and the UI handles WLITHO wrap/unwrap explicitly. This drops
  Router02's payable-native handling and its wrap/unwrap edge cases.
• 0.8 port keeps the intentional overflow of V2 (uint32 timestamp + TWAP price
  accumulators) inside unchecked blocks; SafeMath is dropped (checked math).

Verification: scripts/dex-e2e.ts drives the full flow on the in-process Hardhat
network — pair creation, first-LP mint (200e18 - MINIMUM_LIQUIDITY), getAmountsOut
matching the 0.30%-fee formula to the wei, swap output == quote, slippage revert,
and remove-liquidity returning the correct post-trade constant-product position.
9/9 checks pass. (A mocha/chai test is included too, but this contracts package
has a pre-existing pnpm dep-linking gap — the existing Lep100.test.ts fails the
same way — so the hardhat-run script is the authoritative check.)

Deployment (deployer key held by the operator, read from env, never in-repo):

• scripts/deploy-dex.ts + a makalu network in hardhat.config.ts -> writes
  deployments/dex-700777.json.
• scripts/seed-dex-liquidity.ts + dex-pairs.example.json -> idempotent,
  balance/allowance-checked liquidity seeding.

Remaining for item 1 (follow-up): explorer lib/swap.ts + /swap page, and the
cross-chain saga composing this swap with the existing MultX bridge.

[github-actions]

Test Results

Package	Passed	Failed	Skipped	Total	Duration
api	no results
indexer	no results
explorer	no results

Coverage

Package	Stmts %	Branch %	Funcs %	Lines %
api	no coverage
indexer	no coverage
explorer	no coverage

_{Generated by ci.yaml for ed93d4260d7ddfee50b0f4d60c7ded169d8ccdd3. Test JSON + coverage HTML are uploaded as run artifacts.}