feat(investment): Daily Script Master, market rate on purchase, broken-period interest as expense

- 09 Daily Script Master now saves to and loads from the backend (sample
  rows removed), with Drop to correct a wrong rate.
- Purchase Entry takes the rate (NAV for a mutual fund) from the newest
  Daily Script Master rate on or before the deal date, shows which rate
  was used, warns when the rate entered is outside the day's low-high,
  and clears the rate when the script has none.
- Broken-period interest paid to the seller is debited to expense GL
  500606 instead of Interest Receivable (RBI UCB Investment Directions,
  para 152, confirmed by Jitendra Sir); Interest Entry labels it so.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/investment/investment-data.ts

@@ -1509,6 +1509,13 @@ export const INVESTMENT_GL_BY_TYPE: Record<InstrumentType, string> = {
   SHARE: '100706'
 };
 
+/** Broken-period interest paid to the seller at purchase — an expense, not part of cost (RBI UCB Investment
+ *  Directions para 152). */
+export const BROKEN_PERIOD_INTEREST_GL: InvestmentGlOption = {
+  glCode: '500606',
+  glName: 'BROKEN PERIOD INTEREST PAID ON INVESTMENTS'
+};
+
 /** Charges on an investment deal — expenses on their own GLs, not part of the book value (Jitendra Sir). */
 export const STAMP_DUTY_GL: InvestmentGlOption = { glCode: '500601', glName: 'STAMP DUTY ON INVESTMENTS' };
 export const BROKERAGE_GL: InvestmentGlOption = { glCode: '500602', glName: 'BROKERAGE ON INVESTMENTS' };
@@ -2161,13 +2168,15 @@ export const LIEN_REASON_MASTER: LienReason[] = [
 /** Daily Script Master (legacy menu "09") — the day's quoted rate per script, entered/imported
  *  every working day. Distinct from Script Market Detail ("13") which also carries YTM/valuation. */
 export interface DailyScriptRate {
+  /** Backend id once saved. */
+  id?: number;
   rateDate: string;
   scriptCode: string;
   scriptName: string;
-  openRate: number;
+  openRate: number | null;
   closeRate: number;
-  highRate: number;
-  lowRate: number;
+  highRate: number | null;
+  lowRate: number | null;
 }
 
 export const DAILY_SCRIPT_RATES: DailyScriptRate[] = [