feat(tri27): Token FFI for TRI-27

[gHashTag]

Sub-Issue #437: Token FFI for TRI-27

Files: src/tri27/token_ffi.zig (NEW, ~400 LOC)

Tasks:

• Create spec/token_ffi.tri
• Generate token_ffi.zig via tri gen
• Define TokenContract interface:
  • balanceOf(address) -> u128
  • transfer(to, amount) -> bool
  • stake(amount, lock_period) -> void
  • unstake() -> u128
  • claimRewards() -> u128
• Implement Web3 RPC calls:
  • encodeCall(contract, method, params)
  • sendTransaction(signer, to, value, data)
  • waitForReceipt(tx_hash)
• Add error handling:
  • Revert by reason
  • Out of gas
  • Network error

Parent: #435