[FEATURE]: Centralize transaction initialization and quote fetching to avoid duplicate RPC calls in the widget

[sach2004]

Feature and its Use Cases

The widget currently initializes transaction state and fetches quote-related data in more than one component.

Both TokenDropdown.jsx and TransactionReview.jsx instantiate Transaction, call init(), and in native-token flows may fetch quote data separately.

Why this matters:

• unnecessary duplicate RPC calls for the same network/token selection
• harder-to-maintain state flow
• greater risk of inconsistent quote or transaction state across components
• makes future additions like preflight validation, allowance checks, and multi-Djed support harder

Expected outcome:

• transaction initialization and quote fetching should be owned by a single layer
• components should consume normalized shared state instead of rebuilding it independently
• the widget should perform one consistent initialization flow per network/token selection

Additional Context

Current evidence from the code:

• stablepay-sdk/src/widget/TokenDropdown.jsx initializes Transaction and may fetch trade data during token selection
• stablepay-sdk/src/widget/TransactionReview.jsx repeats transaction initialization and quote fetching in its own effect

A cleaner design would move this into context and expose:

• loading state
• quote state
• normalized transaction details
• initialization errors

This would also pair well with current and future payment-flow work like stablecoin balance checks, fee configuration cleanup, and support for additional Djed variants.

Code of Conduct

• I have joined the Discord server and will post updates there
• I have searched existing issues to avoid duplicates