Add Tempo chain support

[0xh3rman]

Fixes #660, adds Tempo with Relay + Uniswap v4. Tempo has no native gas token
(eth_getBalance is a sentinel, CALLVALUE is always 0; fees are USD-denominated but paid
in 6-dec TIP-20 stablecoins), so this is not a standard chain addition:

1. New ChainStack::Tempo — all behavior keys off is_tempo_stack(), no per-chain branching
2. Native asset = pathUSD (Celo native-is-an-ERC20 mechanism): balance via balanceOf,
   native sends encode ERC-20 transfer(), native swaps use the tokenized-native path
3. Tempo Transaction (0x76): swaps sign as one atomic tx with calls = [approve, swap]
   and explicit fee_token; transfers/approvals stay type-2 (TIP-20 methods auto-pay in the token)
4. Dynamic fee asset: fee_asset_id crosses UniFFI with the fee ceil-scaled to the fee
   token's decimals (gas values stay 18-dec for signing); resolution follows the spec precedence —
   FeeManager userTokens() preference → USD-currency() transfer auto-selection → pathUSD;
   explicit swap fee tokens restricted to fee-eligible pathUSD/USDC.e (fee AMM rejects e.g. cbBTC)
5. Both apps consume the fee asset for display/validation; max-send subtracts the fee when paid
   from the sent token; single fee rate (priority is always 0) hides the picker
6. RPC/indexing: 0x76 calls[] objects decode without failing blocks (last call = primary action),
   receipt feeToken mapped, indexed/confirmed fees scaled to the fee asset,
   inbound pathUSD logs keep the native asset identity
7. AssetType::TIP20 + Postgres ALTER TYPE migration
8. Uniswap v4 swap gas fallback 900k for tempo-stack (250k per new storage slot, first swap ~495k observed)