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-masters/investment-masters.component.html

@@ -225,7 +225,7 @@
               <td>{{ p.city || '—' }}</td>
               <td>{{ p.bankType || '—' }}</td>
               <td>{{ p.glCode ? p.glCode + ' — ' + glName(p.glCode) : '—' }}</td>
-              <td class="num">{{ p.limit != null ? '₹' + (p.limit | number: '1.0-0') : '—' }}</td>
+              <td class="num">{{ (p.limit ?? null) !== null ? '₹' + (p.limit | number: '1.0-0') : '—' }}</td>
               <td>{{ p.cpBankName ? p.cpBankName + (p.cpIfsc ? ' / ' + p.cpIfsc : '') : '—' }}</td>
               <td>{{ p.status ?? 'ACTIVE' }}</td>
             </tr>
@@ -545,10 +545,11 @@
             <th class="num">High</th>
             <th class="num">Low</th>
             <th class="num">Close</th>
+            <th></th>
           </tr>
         </thead>
         <tbody>
-          @for (r of dailyScriptRates; track r.rateDate + r.scriptCode) {
+          @for (r of dailyScriptRates; track r.id ?? r.rateDate + r.scriptCode) {
             <tr>
               <td>{{ r.rateDate }}</td>
               <td>
@@ -559,6 +560,13 @@
               <td class="num">{{ r.highRate | number: '1.2-2' }}</td>
               <td class="num">{{ r.lowRate | number: '1.2-2' }}</td>
               <td class="num">{{ r.closeRate | number: '1.2-2' }}</td>
+              <td>
+                <button type="button" class="pg-btn pg-btn--ghost" (click)="dropDailyRate(r)">Drop</button>
+              </td>
+            </tr>
+          } @empty {
+            <tr>
+              <td colspan="8" class="pg-empty">No rates entered yet.</td>
             </tr>
           }
         </tbody>