Change Liquid Bitcoin ticker to LBTC and tLBTC

[miketlk]

Summary

This PR updates the Liquid Bitcoin tickers in the hardware wallet application to align with the latest naming convention adopted by the Liquid Federation. The mainnet and regtest ticker is changed from L-BTC to LBTC, and the testnet ticker from tL-BTC to tLBTC.

Related Issues

• Closes 🌟 [FEATURE] Change Liquid Bitcoin ticker from L-BTC to LBTC #8
• Related to ElementsProject/elements#1373

Changes

• Updated all user-visible references from L-BTC to LBTC
• Updated testnet references from tL-BTC to tLBTC

Testing

• Confirmed UI displays the updated tickers correctly on mainnet, testnet, and regtest
• Ran existing unit tests to ensure no regressions
• Manual inspection of address/network selection screens and transaction signing previews

Checklist

• Code builds without errors
• Tests added or updated
• Documentation updated (if needed)
• Code reviewed for security and edge cases

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Flag	Coverage Δ
unittests	82.26% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/liquid/liquid_assets.c	60.00% <ø> (ø)

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