Add packages/savings-sdk and packages/savings-widget

[Copilot]

Implements the GoodDollar savings/staking widget from scratch in GoodWidget, reimagining the reference Lit webcomponent as a React mini-app using local @goodwidget/ui primitives and a new viem-based SDK package.

packages/savings-sdk (@goodwidget/savings-sdk)

Thin viem wrapper for the GoodDollar staking contract on Celo mainnet (0x799a23dA264A157Db6F9c02BE62F82CE8d602A45, chain id 42220). Requires viem ≥2 as a peer.

• GooddollarSavingsSDK — getGlobalStats(), getUserStats(), stake(), unstake(), claimReward() (all with optional onHash callback)
• GlobalStats / UserStats types
• formatG$ / parseG$ formatting utilities

packages/savings-widget (@goodwidget/savings-widget)

• SavingsWidget — root component; wraps GoodWidgetProvider and accepts the standard provider, config, themeOverrides, defaultTheme props
• useSavingsSDK — bridges the EIP-1193 provider from useWallet() into viem PublicClient + WalletClient; polls every 30 s
• SavingsInner — Stake/Unstake tab UI with amount input (MAX button, balance display, inline validation), unclaimed rewards + Claim row, staking stats card, and Toast feedback for every async state transition
• SavingsWidgetElement / gw-savings — Shadow DOM custom element and auto-register entry points

// React
<SavingsWidget provider={window.ethereum} defaultTheme="light" />

// Plain HTML
import '@goodwidget/savings-widget/register'
// <gw-savings></gw-savings>

All styled components use createComponent() with unique name values, making every surface overridable via themeOverrides. No direct tamagui imports in the widget layer — all primitives come through @goodwidget/ui.

[Copilot]

@sirpy Unfortunately, I hit an error while trying to use the custom Copilot setup steps configured for this repository and had to close this PR. The error I am seeing is:

no `copilot-setup-steps` job found in your `copilot-setup-steps.yml` workflow file. Please ensure you have a single job named `copilot-setup-steps`. For more details, see https://gh.io/copilot/actions-setup-steps

Once you or someone with the necessary access fixes the problem, please unassign and then reassign issue #0 to me and I'll retry. Thanks!