feat(statics): add TestingLinearTokenOnboarding (eth:tlto) token

[bitgo-ai-agent-dev]

What

• Add 'eth:tlto' to the UnderlyingAsset enum in base.ts (alphabetical, before 'eth:tlton')
• Add terc20() factory call in erc20Coins.ts for the on-chain token (UUID 97753436-903b-4131-82b2-6deea76a5e17, 6 decimals, contract 0x1234567890abcdef1234567890abcdef12345678)
• Add ofcerc20() factory call in ofcErc20Coins.ts for the OFC token (UUID d38204a7-b670-414e-9f58-e2df4798070c)

Why

• Placeholder token/contract for validating the Linear ticket execution route of the token-onboarding pipeline. Test-environment only — no mainnet or staging data provided. Required to unblock downstream indexer-token-add and subsequent onboarding steps under the parent epic SCAAS-10475.

Decision log

1. Placement of terc20() in erc20Coins.ts: Inserted after the last terc20() call using the default eth testnet (kovan), before the holesky/hoodi-specific blocks. Options: (A) insert at the very end of the file before hteth: entries, (B) insert after the last kovan-default terc20. Chose B — keeps testnet entries grouped by default network and avoids mixing eth and hteth blocks.

2. Placement of ofcerc20() in ofcErc20Coins.ts: Placed in tOfcErc20Coins (the test OFC array, after the last ofceth: entry). Token is test-only, so tOfcErc20Coins is the correct array. The symbol 'ofc:eth:tlto' follows the ticket specification exactly.

3. 'eth:tlto' enum position: Inserted alphabetically just before 'eth:tlton' — tlto < tlton since the prefix matches and the shorter string sorts first.

Test plan

• tsc --noEmit on @bitgo/statics passes (no TypeScript errors)
• eslint on changed files passes (no lint errors)
• Only base.ts, erc20Coins.ts, ofcErc20Coins.ts modified — no other files touched
• Contract address is lowercase
• No existing entries modified or removed

Out of scope

None.

Ticket: SCAAS-10476

[linear-code]

SCAAS-10476

[bitgo-ai-agent-dev]

@claude please review this PR