Objective Editor: Improvements

The objective editor has had a clean-up pass: control over how the value is labelled, a friendlier display picker, and reworked drawdown tracking.

Value labels — for money and R-multiple metrics you can now choose Auto or a Custom unit (e.g. R, pips), and put it before or after the number. A live preview shows exactly how the value will read on the widget.
Reworked drawdown objectives:
- Max Drawdown Limit (renamed from "Drawdown Limit") now measures static drawdown — how far your current net P/L sits below your starting balance. While you're net up it reads 0.
- New Daily Drawdown Limit — today's net loss (UTC day) against a daily loss limit.
Date-range filter presets — date filters in the objective, calendar and chart editors now offer live presets like this week to date and this month to date, alongside fixed ranges.