feat: Implement Sign Request Manager component for handling sign requests in the popup (WIP)

- Added SignRequestManager.js to manage sign requests, including UI states for keyspace lock, mismatch, and approval.
- Implemented methods for loading state, rendering UI, and handling user interactions (approve/reject requests).
- Integrated background message listeners for keyspace unlock events and request updates.

crypto_vault_extension/styles/popup.css

@@ -1069,4 +1069,195 @@ input::placeholder, textarea::placeholder {
 .verification-icon svg {
   width: 20px;
   height: 20px;
+}
+
+/* Sign Request Manager Styles */
+.sign-request-manager {
+  margin-top: 16px;
+  padding: 16px;
+  background: var(--bg-secondary);
+  border-radius: 8px;
+  border: 1px solid var(--border-color);
+}
+
+.connection-status {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  margin-bottom: 12px;
+  font-size: 12px;
+  font-weight: 500;
+}
+
+.status-indicator {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  background: #ef4444;
+}
+
+.connection-status.connected .status-indicator {
+  background: #10b981;
+}
+
+.no-requests {
+  text-align: center;
+  padding: 20px;
+  color: var(--text-secondary);
+}
+
+.unlock-prompt, .keyspace-mismatch {
+  text-align: center;
+  padding: 20px;
+}
+
+.unlock-prompt h3, .keyspace-mismatch h3 {
+  margin: 0 0 12px 0;
+  font-size: 16px;
+  color: var(--text-primary);
+}
+
+.unlock-prompt p, .keyspace-mismatch p {
+  margin: 8px 0;
+  color: var(--text-secondary);
+  font-size: 14px;
+}
+
+.hint {
+  font-style: italic;
+  font-size: 12px !important;
+  color: var(--text-tertiary) !important;
+}
+
+.requests-header {
+  margin-bottom: 12px;
+}
+
+.requests-header h3 {
+  margin: 0;
+  font-size: 16px;
+  color: var(--text-primary);
+}
+
+.requests-list {
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+}
+
+.sign-request-card {
+  background: var(--bg-primary);
+  border: 1px solid var(--border-color);
+  border-radius: 6px;
+  padding: 12px;
+}
+
+.request-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: 8px;
+}
+
+.request-id {
+  font-family: monospace;
+  font-size: 12px;
+  color: var(--text-secondary);
+  font-weight: 500;
+}
+
+.request-time {
+  font-size: 11px;
+  color: var(--text-tertiary);
+}
+
+.request-message {
+  margin-bottom: 12px;
+}
+
+.request-message label {
+  display: block;
+  font-size: 12px;
+  font-weight: 500;
+  color: var(--text-secondary);
+  margin-bottom: 4px;
+}
+
+.message-content {
+  background: var(--bg-secondary);
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  padding: 8px;
+  position: relative;
+}
+
+.message-preview {
+  font-family: monospace;
+  font-size: 11px;
+  color: var(--text-primary);
+  word-break: break-all;
+  line-height: 1.4;
+  max-height: 60px;
+  overflow: hidden;
+}
+
+.message-content.expanded .message-preview {
+  max-height: none;
+}
+
+.expand-message {
+  position: absolute;
+  top: 4px;
+  right: 4px;
+  background: var(--accent-color);
+  color: white;
+  border: none;
+  border-radius: 3px;
+  padding: 2px 6px;
+  font-size: 10px;
+  cursor: pointer;
+  transition: background-color 0.2s;
+}
+
+.expand-message:hover {
+  background: var(--accent-hover);
+}
+
+.request-actions {
+  display: flex;
+  gap: 8px;
+  justify-content: flex-end;
+}
+
+.btn-approve, .btn-reject {
+  padding: 6px 12px;
+  border: none;
+  border-radius: 4px;
+  font-size: 12px;
+  font-weight: 500;
+  cursor: pointer;
+  transition: all 0.2s;
+}
+
+.btn-approve {
+  background: #10b981;
+  color: white;
+}
+
+.btn-approve:hover:not(:disabled) {
+  background: #059669;
+}
+
+.btn-reject {
+  background: #ef4444;
+  color: white;
+}
+
+.btn-reject:hover:not(:disabled) {
+  background: #dc2626;
+}
+
+.btn-approve:disabled, .btn-reject:disabled {
+  opacity: 0.6;
+  cursor: not-allowed;
 }