Enhance take-profit and stop-loss input calculations

[taherdhanera]

Closes #17.

Requesting consideration for this bounty.

Changes:

• Adds direction-aware +1%, +2%, and +5% TP/SL move presets for long and short orders.
• Keeps target price, P/L percent, and P/L amount in the selected collateral asset synchronized through a shared calculation helper.
• Uses the current limit price when present, otherwise the live market price, as the TP/SL entry basis.
• Leaves order submission semantics unchanged by continuing to submit only the existing TP/SL target prices.
• Adds deterministic calculation checks for long/short TP and SL conversions.

Validation:

• npm run test:tpsl
• npm run build
• git diff --check
• Served the built app locally and confirmed the index responds with the generated bundle reference.

Payment details can be provided if selected.

[taherdhanera]

Note on checks: the Vercel status is failing with Account is blocked and links to Vercel account-block documentation, not to a build/test error. Local validation passed with npm run test:tpsl, npm run build, git diff --check, and a built-app local smoke check.