feat(FeeEstimator): fee shown in stroops only, no high-fee warning badge, no landmark role for keyboard navigation

[k-deejah]

Problem

Three issues affect FeeEstimator display, context, and integration with TransactionsScreen.

1. FeeEstimator fee values are in "stroops" but most users think in XLM

The fee display shows "100 stroops" and "200 stroops". Most Stellar users know XLM, not stroops. Displaying the equivalent XLM value (stroops / 10,000,000) alongside the stroops value would be more user-friendly.

2. FeeEstimator has no visual indication when the fee has spiked above normal

A fee of 10,000 stroops recommended suggests network congestion. There is no visual warning (e.g. an orange badge or warning icon) when the recommended fee is significantly above the base fee (e.g. >2x). Users are not alerted to unusual network conditions.

3. FeeEstimator is not keyboard-focusable as a landmark region

FeeEstimator renders as a styled div with no region role or aria-label. Keyboard users navigating by landmark cannot jump directly to the fee section. It should have role="region" and aria-label="Network fee estimate".

Solution

1. Add a secondary display "(≈ 0.00001 XLM)" below the stroops value using parseInt(value) / 10_000_000.
2. Add an orange warning badge reading "High fee" when parseInt(recommended) > parseInt(baseFee) * 2.
3. Add role="region" and aria-label="Network fee estimate" to the FeeEstimator root div.

Acceptance Criteria

• XLM equivalent is shown alongside each fee value
• "High fee" orange badge appears when recommended > 2× base fee
• FeeEstimator root has role="region" and aria-label="Network fee estimate"
• npm run build passes

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Note for Contributors: Write a clear PR description. Include a screenshot of the high-fee warning badge and the XLM equivalent display.