feat: add USDC send examples (AA + non-AA) across JS, Go, Python

[Rshahatit]

Summary

Resolves ENG-7711. The example repo previously only demonstrated native-token sends, which left customers hand-building ERC-20 transactions (see the linked support thread — the customer hit repeated "insufficient balance" errors). These examples use the enclave POST /v1/assets/send endpoint, which builds, signs, and broadcasts the transfer for you, and cover both account-abstraction and standard flows.

Each language demonstrates:

• AA flow (sponsorGas omitted/true): Portal sponsors the gas. Requires an Account Abstraction client (isAccountAbstracted: true at signup). The wallet does not need to hold native tokens.
• Non-AA flow (sponsorGas: false): a standard wallet pays its own gas and must hold the chain's native token — the exact "insufficient balance" gotcha from the support thread.

The token field uses the "USDC" shorthand (the enclave resolves it to the right ERC-20 per chain); a contract-address fallback is documented for chains where the shorthand isn't supported.

Changes

Language	What	Run
JavaScript	Javascript/eth-send-assets.js generalized to send USDC (and any token) with AA/non-AA variants — folded into the existing assets/send example rather than a new file	yarn sendUsdc / yarn sendUsdcSponsored
Go	new Go/sendUsdc/sendUsdc.go + Go/cmd/sendUsdc/main.go	make sendUsdc / make sendUsdcSponsored
Python	new Python/send_usdc.py	python send_usdc.py [sponsored]

READMEs updated in each folder with run steps for both flows, the native-gas requirement, and a Circle-faucet pointer.

Security hardening

The JS folder's .gitignore excluded clientApiKey.txt/shares.txt, but Go and Python did not — so anyone running those examples could have committed wallet credentials to this public repo. Added clientApiKey.txt, shares.txt, and backupShares.txt to both Go/.gitignore and Python/.gitignore.

Verification

Static checks: Go build/vet/gofmt, JS node --check, Python py_compile all pass.

Live end-to-end on Sepolia — all three languages confirmed on-chain:

• JS non-AA: wallet paid its own gas, sent 1 USDC — real tx 0x064cc6…acc50 (status 1).
• JS AA: sent USDC while holding 0 ETH → gas sponsored; smart account deployed on first send (UserOp).
• Go AA: make sendUsdcSponsored — balance dropped on-chain (UserOp 0x2020d3…b5d4).
• Python AA: python send_usdc.py sponsored — balance dropped on-chain (UserOp 0x845eeb…969d).

AA sends return a UserOperation hash (verify on a UserOp explorer like JiffyScan, not Etherscan). The non-AA path is the same code with sponsorGas: false, proven by the JS non-AA real tx above.