fix(ui): promote modal overlay to token, lift modal above grain, dedupe FilesPage drop-zone

- Add --color-overlay-dim token to app.css @theme (rgba(15,14,12,0.7) dark, rgba(26,24,22,0.55) light); mirror as --overlay-dim in design-system/colors_and_type.css.
- MorningTriageModal: replace inlined rgba scrim with var(--color-overlay-dim), drop backdrop-blur-sm (brand opposes glassmorphism by default), bump container to z-[60] so it sits above the .grain z-50 overlay.
- FilesPage: collapse two near-identical drop-zone blocks into one bordered region with conditional inner content; preserves isDragOver hover behaviour and aria region.

src/lib/pages/FilesPage.svelte

@@ -155,43 +155,31 @@
   <!-- Drop zone -->
   <div class="px-7 pb-3">
     <Card>
-      {#if !fileTranscript && !transcribing}
-        <div
-          class="flex flex-col items-center justify-center py-10 px-6 rounded-xl border-2 border-dashed m-3
-            {isDragOver
-              ? 'border-accent bg-accent-subtle scale-[1.01]'
-              : 'border-border hover:border-text-tertiary'}"
-          style="transition-duration: var(--duration-ui)"
-          role="region"
-        >
+      <div
+        class="flex flex-col items-center justify-center py-10 px-6 rounded-xl border-2 border-dashed m-3
+          {isDragOver
+            ? 'border-accent bg-accent-subtle scale-[1.01]'
+            : 'border-border hover:border-text-tertiary'}"
+        style="transition-duration: var(--duration-ui)"
+        role="region"
+      >
+        {#if !fileTranscript && !transcribing}
           <EmptyState
             icon={Upload}
             message="Drop an audio file or click to browse"
           />
-          <p class="text-[11px] text-text-tertiary text-center mt-1.5">
-            MP3, WAV, M4A, MP4, FLAC, OGG
-          </p>
-        </div>
-      {:else}
-        <div
-          class="flex flex-col items-center justify-center py-10 px-6 rounded-xl border-2 border-dashed m-3
-            {isDragOver
-              ? 'border-accent bg-accent-subtle scale-[1.01]'
-              : 'border-border hover:border-text-tertiary'}"
-          style="transition-duration: var(--duration-ui)"
-          role="region"
-        >
+        {:else}
           <div class="w-10 h-10 rounded-full bg-bg-elevated flex items-center justify-center mb-3">
             <Upload size={20} class="text-text-tertiary" aria-hidden="true" />
           </div>
           <p class="text-[13px] text-text-secondary text-center">
             Drop audio or video files here
           </p>
-          <p class="text-[11px] text-text-tertiary text-center mt-1.5">
-            MP3, WAV, M4A, MP4, FLAC, OGG
-          </p>
-        </div>
-      {/if}
+        {/if}
+        <p class="text-[11px] text-text-tertiary text-center mt-1.5">
+          MP3, WAV, M4A, MP4, FLAC, OGG
+        </p>
+      </div>
     </Card>
   </div>