feat(investment): Interest Entry screen with coupon and provision schedule

Replace the dummy interest calculation tab with the real Interest Entry:
pick Type / Script / Deal No and Retrieve the holding's schedule from
the backend - every half-yearly coupon and every 31 Mar / 30 Sep closing
provision up to maturity, with days (30/360), gross interest, amount
already booked, net income and the Dr/Cr entry per line. Display only;
nothing is posted to GL yet.

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

src/app/investment/investment.service.ts

@@ -169,6 +169,14 @@ export class InvestmentService {
     return this.http.get<InvestmentPurchaseDto[]>('/investment/purchases');
   }
 
+  /** Coupon and 31 Mar / 30 Sep provision lines of a holding up to maturity (calculated, not posted). */
+  getInterestSchedule(purchaseId: number, asOnDate?: string): Observable<InvestmentInterestScheduleDto> {
+    const params = asOnDate ? `?asOnDate=${encodeURIComponent(asOnDate)}` : '';
+    return this.http.get<InvestmentInterestScheduleDto>(
+      `/investment/purchases/${purchaseId}/interest-schedule${params}`
+    );
+  }
+
   createPurchase(body: object): Observable<{ resourceId: number; resourceIdentifier: string }> {
     return this.http.post<{ resourceId: number; resourceIdentifier: string }>('/investment/purchases', body);
   }
@@ -292,6 +300,42 @@ export function toHolding(p: InvestmentPurchaseDto): InvestmentHolding {
   };
 }
 
+/** One line of a holding's interest schedule (see InvestmentInterestScheduleData in the backend). */
+export interface InvestmentInterestRowDto {
+  type: 'COUPON' | 'PROVISION';
+  intDate: string;
+  fromDate: string;
+  toDate: string;
+  days: number;
+  grossInterest: number;
+  alreadyBooked: number;
+  amount: number;
+  due: boolean;
+}
+
+export interface InvestmentInterestScheduleDto {
+  purchaseId: number;
+  dealNo: string;
+  certNo: string;
+  scriptCode: string;
+  scriptDesc: string;
+  faceValue: number;
+  unitValue: number;
+  balanceUnits: number;
+  purchaseRate: number;
+  bookValue: number;
+  intRate: number;
+  dealDate: string;
+  lastIntDate: string;
+  maturityDate: string;
+  purchasedAccruedInterest: number;
+  couponPerHalfYear: number;
+  asOnDate: string;
+  interestGlCode: string;
+  interestGlName: string;
+  rows: InvestmentInterestRowDto[];
+}
+
 /** The first validation / domain-rule message from a Fineract error response, for a toast. */
 export function apiErrorMessage(err: unknown): string {
   const e = err as HttpErrorResponse;