Implement code review fixes and improvements

- Move admin credentials from hardcoded values to configuration
- Add rate limiting (5/min) to login endpoint for brute force protection
- Extract CleanJsonResponse to shared JsonResponseHelper class
- Add DateHelpers.MonthsBetween utility and consolidate date calculations
- Update PdfReportService to use ScoreThresholds constants
- Remove 5 unused shared components (EmploymentTable, FlagsList, etc.)
- Clean up unused CSS from MainLayout.razor.css
- Create IPdfReportService interface for better testability
- Add authentication requirement to Hangfire dashboard in development
- Seal EducationVerifierService class

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/TrueCV.Web/Components/Layout/MainLayout.razor.css

@@ -1,81 +1,3 @@
-.page {
-    position: relative;
-    display: flex;
-    flex-direction: column;
-}
-
-main {
-    flex: 1;
-}
-
-.sidebar {
-    background-image: linear-gradient(180deg, rgb(5, 39, 103) 0%, #3a0647 70%);
-}
-
-.top-row {
-    background-color: #f7f7f7;
-    border-bottom: 1px solid #d6d5d5;
-    justify-content: flex-end;
-    height: 3.5rem;
-    display: flex;
-    align-items: center;
-}
-
-    .top-row ::deep a, .top-row ::deep .btn-link {
-        white-space: nowrap;
-        margin-left: 1.5rem;
-        text-decoration: none;
-    }
-
-    .top-row ::deep a:hover, .top-row ::deep .btn-link:hover {
-        text-decoration: underline;
-    }
-
-    .top-row ::deep a:first-child {
-        overflow: hidden;
-        text-overflow: ellipsis;
-    }
-
-@media (max-width: 640.98px) {
-    .top-row {
-        justify-content: space-between;
-    }
-
-    .top-row ::deep a, .top-row ::deep .btn-link {
-        margin-left: 0;
-    }
-}
-
-@media (min-width: 641px) {
-    .page {
-        flex-direction: row;
-    }
-
-    .sidebar {
-        width: 250px;
-        height: 100vh;
-        position: sticky;
-        top: 0;
-    }
-
-    .top-row {
-        position: sticky;
-        top: 0;
-        z-index: 1;
-    }
-
-    .top-row.auth ::deep a:first-child {
-        flex: 1;
-        text-align: right;
-        width: 0;
-    }
-
-    .top-row, article {
-        padding-left: 2rem !important;
-        padding-right: 1.5rem !important;
-    }
-}
-
 #blazor-error-ui {
     background: lightyellow;
     bottom: 0;
@@ -88,9 +10,9 @@ main {
     z-index: 1000;
 }
 
-    #blazor-error-ui .dismiss {
-        cursor: pointer;
-        position: absolute;
-        right: 0.75rem;
-        top: 0.5rem;
-    }
+#blazor-error-ui .dismiss {
+    cursor: pointer;
+    position: absolute;
+    right: 0.75rem;
+    top: 0.5rem;
+}