Enhance signature handling and annotation features

- Added dependency injection for `AnnotationService`, `DocumentService`, and `AuthService` in `ReportViewer.razor`.
- Improved signature button logic with dynamic appearance and feedback.
- Introduced annotation checkbox overlays for marking signature fields.
- Refactored signature saving and application logic into `SaveSignatureAsync` and `SubmitSignaturesAsync`.
- Added `BuildFreshBaseReport` and `AddAnnotationPlaceholders` for dynamic report creation.
- Implemented annotation-specific signature placement with `AddSignatureAtAnnotation`.
- Enhanced state management for annotations and signature overlays.
- Updated `app.css` with styles for annotation checkboxes.
- Added cache-control headers and versioned JavaScript in `index.html`.
- Improved `receiver-signature.js` with annotation checkbox management, optimized signature pad logic, and debugging utilities.
- Performed general code cleanup and optimization for maintainability.

EnvelopeGenerator.ReceiverUI/wwwroot/css/app.css

@@ -70,4 +70,65 @@ article {
 .dx-blazor-reporting-container {
     height: calc(100vh - 130px) !important;
     width: 100% !important;
+}
+
+/* ── Force DevExpress viewer pages into a single centered column ─────────── */
+.dxbrv-report-preview-content {
+    display: flex !important;
+    flex-direction: column !important;
+    align-items: center !important;
+}
+
+/* ── Annotation signature checkbox overlays ─────────────────────────────── */
+.annot-sig-cb-wrapper {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    gap: 8px;
+    border-radius: 4px;
+    font-size: 0.82rem;
+    font-weight: 700;
+    font-family: "Segoe UI", Arial, sans-serif;
+    padding: 0 10px;
+    overflow: hidden;
+    transition: background-color 0.15s, border-color 0.15s, box-shadow 0.15s;
+    box-shadow: 0 2px 6px rgba(0,0,0,0.25);
+    background-color: rgba(255, 236, 153, 0.97);
+    border: 2px dashed #e65100;
+    color: #5d2600;
+    user-select: none;
+}
+
+.annot-sig-cb-wrapper:hover {
+    background-color: rgba(255, 213, 79, 1);
+    border-color: #bf360c;
+    box-shadow: 0 3px 10px rgba(230, 81, 0, 0.4);
+}
+
+.annot-sig-cb-wrapper--checked {
+    background-color: rgba(200, 230, 201, 0.97);
+    border: 2px solid #2e7d32;
+    color: #1b5e20;
+    box-shadow: 0 1px 4px rgba(46, 125, 50, 0.25);
+}
+
+.annot-sig-cb-wrapper--checked:hover {
+    background-color: rgba(165, 214, 167, 1);
+    border-color: #1b5e20;
+    box-shadow: 0 3px 10px rgba(46, 125, 50, 0.35);
+}
+
+.annot-sig-cb {
+    width: 18px;
+    height: 18px;
+    flex-shrink: 0;
+    cursor: pointer;
+    accent-color: #2e7d32;
+}
+
+.annot-sig-cb__label {
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    pointer-events: none;
 }