Add Horizon API error recovery with exponential backoff

[therealjhay]

Description: When the Stellar Horizon API is temporarily unavailable or rate-limited, the app should retry with exponential backoff instead of immediately showing an error. This is especially important for balance refresh and transaction history.

Requirements:

• Add a retry utility with exponential backoff (1s, 2s, 4s, 8s, max 30s)
• Apply to Horizon API calls in the wallet store and any transaction fetching
• Show a "Reconnecting..." indicator during retries
• After 3 failed retries, show the error with a manual "Retry" button
• Log retry attempts for debugging

Suggested execution steps:

1. Create lib/utils/retry.ts with a generic retryWithBackoff(fn, options) function
2. In lib/store/walletStore.ts, wrap the refreshBalances Horizon call with retry
3. Add a isReconnecting state to the store
4. In the wallet page, show a subtle "Reconnecting..." banner when isReconnecting is true
5. After max retries, show the error with a manual "Retry" button

Example commit message:

feat(stellar): add exponential backoff retry for Horizon API calls

Created retryWithBackoff utility with 1s→2s→4s→8s→max 30s backoff.
Applied to wallet balance refresh and all Horizon API calls. Shows
"Reconnecting..." indicator during retries, manual "Retry" on failure.

[devOgazi]

@devOgazi has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Please assign me I can work on this

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[ABEEGOLD]

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I would like to work on this issue because i can do it.

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[adetomiwa21]

@adetomiwa21 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Kindly assign me this issue , thank you

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