Show liquidation prices on chart

[JeremyZeng77]

Fixes #7

Summary

• Add a separate user setting for liquidation price lines on the chart.
• Draw dashed liquidation price lines for positions in the selected market.
• Recalculate and redraw liquidation lines when funding tracker data updates, matching the position-table liquidation formula.

Verification

• git diff --check
• npm run build (passes; existing Svelte/a11y/dependency warnings remain)

Bounty / payout

Requesting assignment and consideration for the crypto bounty on #7.

Preferred payout: USDT TRC20 TWupTAoFjxR2VmqUUvzhfmUwXVZR6Kvz1Y
Backup payout: PayPal https://paypal.me/Jeremytsangchina

[JeremyZeng77]

Verification note: the Vercel status failure reports "Account is blocked." Local validation for this branch passed with git diff --check and npm run build; the build completed with existing Svelte/a11y/dependency warnings.