Merge branch 'feat/desktop-reader-brightness' into chore/reconcile-ui-review

frontend/src/routes/manga/[id]/chapter/[chapter_id]/+page.svelte

@@ -1094,6 +1094,28 @@
 
         {/if}
 
+        <!-- Desktop brightness. On mobile this control lives in the reader
+             settings sheet; desktop has no sheet, so it sits inline here.
+             Shares the `brightness` state and the same `--reader-dim`
+             effect, so a value set on either form factor stays in sync. -->
+        <label class="brightness-field desktop-control">
+            <Sun size={16} aria-hidden="true" />
+            <span class="visually-hidden">Brightness</span>
+            <input
+                type="range"
+                class="brightness-slider"
+                min="0.3"
+                max="1"
+                step="0.05"
+                value={brightness}
+                oninput={(e) => {
+                    brightness = Number((e.currentTarget as HTMLInputElement).value);
+                }}
+                aria-label="Brightness"
+                data-testid="reader-brightness-desktop"
+            />
+        </label>
+
         <button
             type="button"
             class="reader-settings-btn mobile-control"
@@ -2181,6 +2203,20 @@
         width: 100%;
     }
 
+    /* Inline desktop brightness control in the reader nav. The slider is
+       full-width inside the mobile settings sheet; here it's capped so it
+       sits neatly beside the mode toggle. */
+    .brightness-field {
+        display: inline-flex;
+        align-items: center;
+        gap: var(--space-2);
+        color: var(--text-muted);
+    }
+
+    .brightness-field .brightness-slider {
+        width: 120px;
+    }
+
     @media (max-width: 640px) {
         /* Reader-nav sits at the viewport top — the global mobile
            chrome is hidden on this route so there's no app bar above