style: improve thumbnail indicator + selection contrast

- Bump primary from #3b6ed8 to #3b82f6 (Tailwind blue-500). Higher
  saturation reads better against both the dark surface and varied
  photo content. Contrast against bg-bg goes from ~5.7:1 to ~6.6:1.
- Selection ring: add ring-offset-2 ring-offset-bg so the bright blue
  has a dark gap separating it from the photo edge — pops on light
  and dark photos alike. Hover ring gets the same treatment.
- Selection check badge: white ring + shadow + thicker stroke so the
  badge is legible against any photo (was disappearing on bright
  scenes).
- Rating stars: wrap in a translucent dark pill with backdrop-blur so
  yellow stars don't vanish on yellow / sandy photos.
- Heap / duplicate / discarded badges: matching white ring + thicker
  icon stroke so they all read consistently and don't blend in.
- Timeline date headers: text-text instead of text-text-muted so the
  group labels actually pop above the grid.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/timeline/PhotoThumbnail.tsx

@@ -118,8 +118,11 @@ export function PhotoThumbnail({
     <div
       className={clsx(
         'group relative cursor-pointer overflow-hidden rounded-sm transition-all duration-200',
-        'hover:ring-2 hover:ring-primary/50',
+        // Two-tone hover ring: bright primary inner + dark offset so it
-        isSelected && 'ring-2 ring-primary shadow-lg',
+        // pops on light AND dark photos.
+        'hover:ring-2 hover:ring-primary/60 hover:ring-offset-1 hover:ring-offset-bg',
+        isSelected &&
+          'ring-2 ring-primary ring-offset-2 ring-offset-bg shadow-lg',
         !imageLoaded && 'bg-surface animate-pulse'
       )}
       style={{
@@ -181,49 +184,52 @@ export function PhotoThumbnail({
         </div>
       )}
       
-      {/* Selection Indicator */}
+      {/* Selection Indicator — white ring around the primary fill so the
+       *  badge stays visible against any photo (light or dark). */}
       {isSelected && (
-        <div className="absolute left-1 top-1 flex h-6 w-6 items-center justify-center rounded-full bg-primary text-white">
+        <div className="absolute left-1 top-1 flex h-6 w-6 items-center justify-center rounded-full bg-primary text-white shadow-md ring-2 ring-white/90">
-          <Check className="h-4 w-4" />
+          <Check className="h-4 w-4" strokeWidth={3} />
         </div>
       )}
 
-      {/* Rating Stars */}
+      {/* Rating Stars — sit in a translucent dark pill so yellow stars
+       *  don't disappear against a yellow / sandy photo. */}
       {photo.rating > 0 && (
-        <div className="absolute bottom-1 left-1 flex gap-0.5">
+        <div className="absolute bottom-1 left-1 flex items-center gap-0.5 rounded bg-black/55 px-1 py-0.5 shadow-sm backdrop-blur-[2px]">
           {Array.from({ length: photo.rating }).map((_, i) => (
             <Star
               key={i}
-              className="h-3 w-3 fill-star text-star"
+              className="h-3 w-3 fill-star text-star drop-shadow"
             />
           ))}
         </div>
       )}
 
-      {/* Flag Indicators */}
+      {/* Flag Indicators — every badge gets a white ring so it survives
+       *  any photo content. */}
       <div className="absolute bottom-1 right-1 flex items-center gap-1">
         {isInActiveHeap && (
           <div
-            className="flex h-5 w-5 items-center justify-center rounded-full bg-pick text-white shadow-md"
+            className="flex h-5 w-5 items-center justify-center rounded-full bg-pick text-white shadow-md ring-2 ring-white/90"
             title="In active heap"
           >
-            <ShoppingBasket className="h-3 w-3" />
+            <ShoppingBasket className="h-3 w-3" strokeWidth={2.5} />
           </div>
         )}
         {photo.is_duplicate && (
           <div
-            className="flex h-5 w-5 items-center justify-center rounded-full bg-black/60 text-white shadow-md"
+            className="flex h-5 w-5 items-center justify-center rounded-full bg-black/70 text-white shadow-md ring-2 ring-white/90"
             title="Duplicate (matches another photo's hash)"
           >
-            <Copy className="h-3 w-3" />
+            <Copy className="h-3 w-3" strokeWidth={2.5} />
           </div>
         )}
         {photo.is_discarded && (
           <div
-            className="flex h-5 w-5 items-center justify-center rounded-full bg-reject text-white shadow-md"
+            className="flex h-5 w-5 items-center justify-center rounded-full bg-reject text-white shadow-md ring-2 ring-white/90"
             title="Discarded"
           >
-            <Trash2 className="h-3 w-3" />
+            <Trash2 className="h-3 w-3" strokeWidth={2.5} />
           </div>
         )}
       </div>

frontend/src/components/timeline/Timeline.tsx

@@ -482,7 +482,7 @@ export function Timeline() {
                   }}
                   className="flex items-end pb-1"
                 >
-                  <h3 className="text-sm font-semibold uppercase tracking-wide text-text-muted">
+                  <h3 className="text-sm font-semibold uppercase tracking-wide text-text">
                     {item.label}
                   </h3>
                 </div>

frontend/src/index.css

@@ -12,7 +12,7 @@
     --color-text: #e8e6e0;
     --color-text-muted: #878580;
     --color-text-faint: #4a4845;
-    --color-primary: #3b6ed8;
+    --color-primary: #3b82f6;
     --color-pick: #4f9e5c;
     --color-reject: #c25a5a;
     --color-star: #d4a340;

frontend/tailwind.config.js

@@ -17,7 +17,7 @@ export default {
         text: '#e8e6e0',
         'text-muted': '#878580',
         'text-faint': '#4a4845',
-        primary: '#3b6ed8', // deep royal blue
+        primary: '#3b82f6', // saturated blue (Tailwind blue-500) — high contrast on dark bg AND on photo content
         pick: '#4f9e5c',    // green for picked
         reject: '#c25a5a',  // red for rejected
         star: '#d4a340',    // amber for stars