feat: emit live Excel formulas for ร.15 revenue-estimate semester rows

Replace static computed values for F/H/J/L/N/P/R with FormulaA1 cell
formulas (=B-D, =(F*10)/100, etc.) so the exported report is auditable
and recalculates in Excel, matching a reference ร15.xlsx. P/R now use
the per-row contribution/framework percent passed from rmutr-api
instead of a fixed 40%.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KhYYmBPw4LhYXoDnTNz2xV

Models/budget/revenue_estimates.cs

@@ -46,6 +46,8 @@ namespace rmutr_report.Models
         public decimal? contribution_central_budget { get; set; }
         public decimal? contribution_central_expenditure { get; set; }
         public decimal? expenditure_limit { get; set; }
+        public decimal? contribution_percent { get; set; }
+        public decimal? framework_percent { get; set; }
 
 
         public int? topic_type { get; set; }