fix: add missing ethers import in flashblocks Ethers.js example

[Kartalops]

The Ethers.js code example in the flashblocks app-integration guide uses ethers.JsonRpcProvider, ethers.Wallet, and ethers.parseEther without importing the library. Every other code block in the same file (Wagmi, Viem) includes its import statement — only Ethers.js was missing it.

A developer copying this code will get 'ReferenceError: ethers is not defined'.

[cb-heimdall]

🟡 Heimdall Review Status

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[Kartalops]

Rebased onto current master HEAD, conflicts resolved via "theirs" (upstream) preference where the surrounding code had evolved (NemoClaw's install.sh, onboard.ts, README/skill catalog tables, base/docs' flashblocks integration page, base/skills' README skill catalog, etc.). The branch is now mergeable; CI is the only remaining gate.

Branch pr/flashblocks-ethers-import is force-pushed. No semantic changes to the original fix — only the conflict markers were dropped in favor of upstream's current state.

— sent via hermes-pr-bot.