More accurate deposit conversions and capacity math

A few number-accuracy fixes landed across estimates, invoices, and the profitability report.

What changed

• Deposit credits no longer undercharge tax. When you convert an accepted estimate that had a paid deposit, the deposit credit is now applied after tax. Previously, on tax-charging estimates, the tax owed on the deposit portion was quietly cancelled — the converted invoice's remaining balance came out low by exactly the tax on the deposit. The final balance now equals the estimate total minus the deposit, to the cent.
• A tax-free estimate stays tax-free when converted. If you quoted an estimate with no tax, converting it no longer sneaks in your default tax rate — the invoice matches the quote the client accepted.
• Utilization no longer over-counts partial time off. On the dashboard and the profitability report, an approved vacation that only partly falls inside the reporting window now reduces capacity by just the days in range, instead of the whole request. Reports that spanned the start or end of a vacation were overstating utilization; they now read true.

Where you'll see it

Estimate-to-invoice conversion, the invoice totals, and the Utilization tab of the Profitability report. Time-off and holiday tables also pick up a small visual tidy — one clean border instead of a doubled one.