feat: first-class XCM transfer helper command

Summary

Add a dot xcm transfer command that abstracts away the complexity of constructing XCM messages for common cross-chain transfer scenarios.

Motivation

Currently, sending an XCM transfer requires manually constructing VersionedLocation, VersionedAssets, and other complex nested types as CLI arguments. This is the #1 source of friction for users doing cross-chain operations.

Example

Instead of:

dot tx XcmPallet.limited_reserve_transfer_assets \
  'V4({parents:1,interior:X1([Parachain(1000)])})' \
  'V4({parents:0,interior:X1([AccountId32({network:null,id:0xd435...})])})' \
  'V4([{id:{parents:0,interior:Here},fun:Fungible(10000000000)}])' \
  0 Unlimited \
  --chain polkadot

Users could write:

dot xcm transfer --from alice --to 5GrwvaEF... --dest asset-hub --amount 10DOT --chain polkadot

Proposed Changes

• New src/commands/xcm.ts: CLI command with ergonomic flags
• New src/core/xcm.ts: Route resolution, type construction for XCM messages
  • Map chain names to parachain IDs
  • Build VersionedLocation from simple chain/account params
  • Build VersionedAssets from human-readable amount strings
  • Support common patterns: relay→parachain, parachain→relay, parachain→parachain
• Tests for type construction and route resolution

Dependencies

• #75 (parachain name resolution) — needed for --dest asset-hub to resolve to Parachain(1000)
• Inspect calls listing — for discovering available XCM pallets/calls per chain
• dot convert — for address format handling

Related Issues

• #13 (RFC: XCM file format) — complementary. The helper is for simple transfers; XCM files are for complex programs.

Priority

P3 — Large feature, defer until foundation is strong. Size L.

Start by reading the proposed src/commands/xcm.ts and src/core/xcm.ts entry points, then review dependency #75, inspect calls listing, and compare address handling with dot convert. Done means supporting the stated common transfer routes and human-readable arguments, with tests covering XCM type construction and route resolution.