style(FN-1847): unify dialog overlay styling and add accessibility attributes

- Add role=dialog and aria-modal attributes to all modal dialogs for accessibility
- Standardize close button aria-labels across all modals
- Unify overlay backdrop-filter, z-index, and background styles in styles.css
- Add light theme overrides for non-standard overlay backgrounds
- Update AgentListModal tests to reflect new aria attributes
- Add changeset for @gsxdsm/fusion package

packages/dashboard/app/styles.css

@@ -3019,6 +3019,10 @@ body {
   width: 640px;
 }
 
+.modal-md {
+  width: min(520px, calc(100vw - 32px));
+}
+
 .modal-header {
   display: flex;
   justify-content: space-between;
@@ -3093,6 +3097,12 @@ body {
   gap: 10px;
 }
 
+.modal-body {
+  padding: var(--space-lg) 20px;
+  overflow-y: auto;
+  flex: 1;
+}
+
 .import-preview-list {
   margin: 8px 0;
   padding-left: 20px;
@@ -6698,13 +6708,18 @@ body {
   }
 
   /* Modal: full-screen on mobile */
-  .modal-overlay {
+  .modal-overlay,
+  .agent-detail-overlay,
+  .agent-dialog-overlay,
+  .chat-new-dialog-backdrop,
+  .workflow-output-modal-overlay {
     padding-top: 0;
     align-items: stretch;
   }
 
   .modal,
-  .modal-lg {
+  .modal-lg,
+  .modal-md {
     width: 100%;
     max-width: 100%;
     height: 100vh;
@@ -10413,7 +10428,12 @@ html .column.drag-over * {
 }
 
 /* Light theme specific overrides */
-[data-theme="light"] .modal-overlay {
+[data-theme="light"] .modal-overlay,
+[data-theme="light"] .agent-detail-overlay,
+[data-theme="light"] .agent-dialog-overlay,
+[data-theme="light"] .mission-manager-overlay,
+[data-theme="light"] .workflow-output-modal-overlay,
+[data-theme="light"] .chat-new-dialog-backdrop {
   background: rgba(31, 35, 40, 0.5);
 }
 
@@ -10425,6 +10445,10 @@ html .column.drag-over * {
   background: rgba(246, 248, 250, 0.6);
 }
 
+[data-theme="light"] .mission-manager__header {
+  background: rgba(246, 248, 250, 0.8);
+}
+
 [data-theme="light"] .settings-sidebar {
   background: rgba(246, 248, 250, 0.6);
 }
@@ -22909,11 +22933,12 @@ html .column.drag-over * {
   left: 0;
   right: 0;
   bottom: 0;
-  background: rgba(0, 0, 0, 0.75);
+  background: rgba(0, 0, 0, 0.6);
+  backdrop-filter: blur(4px);
   display: flex;
   align-items: center;
   justify-content: center;
-  z-index: 1000;
+  z-index: 100;
   padding: var(--space-lg, 16px);
 }
 
@@ -24133,10 +24158,11 @@ html .column.drag-over * {
   position: fixed;
   inset: 0;
   background: rgba(0, 0, 0, 0.6);
+  backdrop-filter: blur(4px);
   display: flex;
   align-items: center;
   justify-content: center;
-  z-index: 1000;
+  z-index: 100;
   padding: 20px;
 }
 
@@ -25511,10 +25537,11 @@ html .column.drag-over * {
   position: fixed;
   inset: 0;
   background: rgba(0, 0, 0, 0.6);
+  backdrop-filter: blur(4px);
   display: flex;
   align-items: center;
   justify-content: center;
-  z-index: 1000;
+  z-index: 100;
   padding: 20px;
 }
 
@@ -28504,11 +28531,12 @@ html .column.drag-over * {
 .chat-new-dialog-backdrop {
   position: fixed;
   inset: 0;
-  background: rgba(0,0,0,0.5);
+  background: rgba(0, 0, 0, 0.6);
+  backdrop-filter: blur(4px);
   display: flex;
   align-items: center;
   justify-content: center;
-  z-index: 200;
+  z-index: 100;
 }
 
 .chat-new-dialog {